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BRIEF  INTRODUCTION 


TO 


Qdalitative  Analysis 


FOR   USE 


IN  INSTRUCTION  IN  CHEMICAL  LABORATORIES. 


BY 

LUD  WIG  j^EDICUS, 

PROFESSOR    OF    CHEMISTRY    IX    THE    UNIVERSITY    AT   WURZBURG. 


TRANSLATED  FROM  THE  TENTH   AND  ELEVENTH  GERMAN 
EDITION,   WITH   ADDITIONS. 


BY 

JOHN   MARSHALL, 

PROFESSOR  OF  CHEMISTRY  AND  TOXICOLOGY  IN  THE  DEPARTMENT  OF  MEDICTNE 
OF  THE  UNIVERSITY   OF  PENNSYLVANIA. 

M5  

'       .  FIFTH  EDITION.  [      D  R.    J.    p.    ^  Jj 


PITILADELPHTA   AND   LONDON: 

PRINTED  BY  J.   B.   LIPPINCOTT  COMPANY. 
1904. 


Copyright,  1891,  by  John  Marshall. 


Copyright,  1903,  by  John  Marshall. 


TRANSLATOR'S   PREFACE. 


The  merit  of  Medicus's  "Qualitative  Analysis,"  and  its 
popularity,  which  is  shown  by  its  having  already  passed 
through  five  editions  in  the  German  language,  led  to  this 
translation. 

The  translator  has  taken  the  liberty  of  rearranging  the 
elements  in  the  first  part  of  the  book  into  groups,  to  corre- 
spond with  their  precipitation  by  group  reagents,  and  also  of 
adding  two  tables  and  amplifying  the  text  to  the  extent  of 
about  forty  pages. 

J.  M. 

Philadelphia,  1892. 


PREFACE  TO  THE  SECOND  EDITION. 


In  the  second  edition  a  number  of  additions  and  changes 
have  been  made  in  the  parts  treating  of  the  methods  of  pro- 
cedure in  the  separation  of  the  bases  into  groups.  A  table 
showing  the  solubility  of  many  of  the  salts  of  the  commonly 
occurring  metals  has  also  been  added. 

J.  M. 

Philadelphia,  1892. 


PREFACE  TO  THE  FOURTH  EDITION. 


Some  chancres  in  the  text  have  been  made  in  the  fourth 
edition,  and  an  additional  method  for  the  separation  of  the 
members  of  the  third  group  has  been  inserted. 

J.  M. 
Philadelphia,  1896. 

8 


PREFACE  TO  THE  FIFTH  EDITION. 


In  this  edition,  which  is  from  the  tenth  and  eleventh  German 
edition,  there  have  been  incorporated  some  general  introductory 
remarks  on  the  theory  and  behavior  of  ions.  Changes  have 
been  made  in  various  parts  of  the  book  to  correspond  with  the 
theory  of  ions.  In  the  fourth  edition  two  methods  were  given 
for  the  separation  of  the  bases  of  the  third  and  fifth  groups. 
Experience  in  the  laboratory  has  determined  which  of  the  two 
methods  of  separation  seemed  better  adapted  for  use  by  students, 
and,  therefore,  in  the  case  of  both  of  these  groups  the  method 
which  seemed  least  adapted  was  omitted  from  the  present  edition. 
To  the  Appendix  have  been  added  two  examples  of  the  behavior 
of  the  rare  elements  contained  in  thorite  and  lead  selenide. 


J.  M. 

Philadelphia,  1903. 


CONTENTS. 


PAGE 
iNTROCrCTION        7 


I. — Properties  of  the  Bases 15 

I.  Group:  Silver,  Mercurous  Salts,  and  Lead 15 

II.  Group :     Mercuric    Salts,     Copper,    Bismuth,    Cadmium, 

Arsenic,  Antimony,  Tin,  Gold,  and  Platinum 22 

III.  Group:  Iron,  Chromium,  Aluminium 46 

IV.  Group :  Manganese,  Zinc,  Nickel,  and  Cobalt 54 

V.  Group :  Barium,  Strontium,  and  Calcium 62 

VI.  Magnesium,  Potassium,  Sodium,  Ammonium,  and  Lithium    66 

II. — Properties  of  the  Acids 73 

I.  Group :  Sulphuric  Acid,  Hydrofluosilicic  Acid 73 

II.  Group:  Sulphurous  Acid,  Hyposulphurous  Acid,  Phos- 
phoric Acid,  Boric  Acid,  Hydrofluoric  Acid,  Carbonic 
Acid,  Silicic  Acid,  Chromic  Acid,  Arsenic  Acid,  Arseni- 
ous  Acid 75 

III.  Group :  Hydrochloric  Acid,  Hydrobromic  Acid,  Hydriodic 

Acid,  Hydrocyanic  Acid,  Hydroferrocyanic  Acid,  Hydro- 
ferricyanic  Acid,  Sulphydric  Acid,  Nitrous  Acid,  Hypo- 
chlorous  Acid 88 

IV.  Group :  Nitric  Acid,  Chloric  Acid 101 

Appendix  :  Acetic  Acid,  Oxalic  Acid,  Tartaric  Acid    .    .    .  103 

III. — Preliminary  Examination 107 

(a)  Preliminary  Tests  in  the  Dry  Way 107 

1.  Examination  in  the  Reduction-Tube 107 

2.  Examination  on  Charcoal 110 

3.  Examination  in  the  Flame 114 

4.  Examination  by  means  of  Microcosmic  Salt,  or  Borax  .    .114 
(J)  Preliminary  Tests  for  Acids 116 

1*  5 


6 

PAGE 

IV.— Solution  and  Fusion 120 

1.  Dissolving  Oxides  and  Salts 121 

2.  Dissolving  Metals  and  Alloys 127 

3.  Sulphides  of  the  Heavy  Metals 128 

4.  Cyanides 128 

5.  Silicates 130 

V. — Detection  of  the  Bases  in  the  Wet  Way 133 

Precipitation  of  the  Different  Groups 133 

First  Group 136 

Second  Group 139 

Third  Group 141 

Fourth  Group 143 

Fifth  Group 144 

Sixth  Group 145 

Separation  of  the  Bases  contained  in  the  Group  Precipitates   .    .  146 

Separation  of  the  First  Group 146 

Separation  of  the  Second  Group 148 

Separation  of  the  Third  Group 159 

Separation  of  the  Fourth  Group 164 

Separation  of  the  Fifth  Group 165 

Separation  of  the  Sixth  Group 168 

VI. — Examination  for  Acids 174 

VH. — Appendix,     Behavior  of  the  Compounds  of  the  Kare  Ele- 
ments     191 

Examples  for  Practice  in  Testing  for  the  Rare  Elements  ....   ]or> 


INTRODUCTION. 


When  the  chemist  has  to  examine  some  compound  or 
mixture  of  unknown  composition,  he  may  put  the  questions, 
What  elements  are  contained  in  the  former  ?  What  are  the 
component  substances  of  the  latter?  The  processes  which 
he  must  use  in  order  to  obtain  the  answers  to  these  ques- 
tions, i.  e.y  to  ascertain  the  elements  and  component  sub- 
stances, belong  to  the  domain  of  Qualitative  Analysis. 

Qualitative  analysis  aims  only  to  determine  what  sub- 
stances are  actually  present,  and  leaves  undetermined  the 
amounts  present.  To  ascertain  the  amounts  is  the  province 
of  Quantitative  Analysis. 

The  object  of  this  book  is  to  treat  of  the  systematic  pro- 
cedure for  the  detection  of  the  bases  and  acids,  together  with 
the  requisite  preliminary  tests  and  the  methods  of  solution 
and  decomposition.  The  systematic  procedure,  however,  is 
preceded  by  a  brief  description  of  the  behavior  of  the  more 
important  bases  and  acids.  The  behavior  of  the  rarer  ele- 
ments is  briefly  described  and  illustrated  by  examples  in 
the  Appendix.  The  atomic  weights  ^^^  are  expressed  first  as 
compared  with  Oxygen  =  16,  and  second,  in  parentheses,  as 
compared  with  Hydrogen  =  1. 

General  Remarks. — All  salts  (the  true  salts,  like  KCl 
and  KNO3,  and  also  the  hydroxyl  salts  or  bases,  as  KOH, 
and  the  hydrogen  salts  or  acids,  as  HCl)  when  in  aque- 
ous   solution    are    more    or  less   separated    into   their   ions. 

Sufficiently  diluted  solutions  of  potassium  chloride,  for  ex- 

4- 
ample,  contain  the  ions ;  i.  e.,  potassium  as  cation  (K  or  K'), 


International. 


8 

on  the  one  hand,  and  chlorine  as  anion  (CI  or  CV),  on  the 
other  hand.  It  is  these  ions  which  enter  into  the  reaction 
and  are  detected  in  most  of  the  analytical  changes.  One 
is  able  to  detect  the  presence  of  chlorine  in  potassium  chlo- 
ride by  means  of  argentic  nitrate — i.  e.,  by  the  silver  ion 
which  is  present  in  the  argentic  nitrate  solution — according 
to  the  equation  : 

KCl  4-  AgNOg  -=  AgCl  +  KNO3, 

i.  e.,  CV  +  Ag  •  =  AgCl  or  CI  +  Ag  =  AgCl. 

The  silver  cation  combines  with  the  chlorine  anion  to  form 
insoluble  argentic  chloride. 

However,  it  is  impossible  in  the  same  manner  to  detect 
the  presence  of  chlorine  in  potassium  chlorate  (KCIO3), 
because  the  aqueous  solution  of  this  substance  contains  no 
chlorine  ions,  but  contains  the  anion  of  chloric  acid,  the 
chlorate  ion  CIO3  or  CIO3'.  In  this  case  the  presence  of 
chlorine  may  be  detected  by  the  silver  ion  if  the  potassium 
chlorate  be  fused  previous  to  its  being  dissolved  in  water. 
In  the  fusion  oxygen  separates  from  the  compound  according 
to  the  equation : 

KC103=KCl-f03. 

On  dissolving  the  fused  mass  in  water  and  treating  the  solu- 
tion with  argentic  nitrate,  argentic  chloride  is  precipitated, 
showing  that  the  solution  must  have  contained  chlorine  ions. 

Only  the  ions  show  the  characteristic  reactions  of  salts  in 
aqueous  solution. 

The  extent  to  which  salts  in  aqueous  solution  are  disso- 
ciated is  variable :  there  are  salts  which  in  dilute  solutions 
are  practically  completely  dissociated — for  example,  potas- 
sium chloride ;  there  are  also  others  which  are  only  slightly 
dissociated — for  example,  mercuric  chloride ;  while  practi- 
cally no  dissociation  whatever  occurs  with  mercuric  cyanide 


9 

in  aqueous  solution,  the  solution  giving  no  response  to  the 
usual  reactions  for  cyanogen  and  for  merciury. 

Of  the  salts,  the  neutral  salts  are  most  strongly  disso- 
ciated. In  aqueous  solution  of  average  concentration  most 
neutral  salts  are  dissociated  to  the  extent  of  over  one-half 
of  the  content  of  the  solution.  The  salts  most  strongly  dis- 
sociated are  those  with  univalent  ions :  salts  with  ions  of 
greater  valence  are  proportionately  less  readily  dissociated 
into  their  ions.  Greater  variations  with  respect  to  the 
degree  of  dissociation  occur  in  the  case  of  the  acids  (hydro- 
gen salts) ;  and  accordingly  diiferentiation  may  be  made 
between  strong,  moderately  strong,  and  weal?:  acids ;  likewise 
between  strong  and  weak  bases  (hydroxyl  salts). 

As  to  which  particular  ions  for  the  time  being  come  into 
play  during  analytical  decompositions,  mention  will  be  made 
under  the  respective  acids  and  bases  :  it  will  be  observed,  for 
example,  that  in  conjunction  with  the  mercurous  ion  Hg* 
there  is  the  mercuric  ion  Hg  *  *,  with  the  ferrous  ion  Fe  * '  the 
ferric  ion  Fe  *  *  * ,  and  that  the  manganate  ion  of  the  salts  of 
manganic  acid  (Mn04'')  is  distinct  from  the  permanganate 
ion  of  the  salts  of  permanganic  acid  (MnO^').  It  will  also 
be  found  that  in  most  of  the  zinc  reactions  the  zinc  ion  Zn ' ' 
takes  part ;  while,  on  the  other  hand,  the  zincate  ion  ZnOg" 
takes  part  in  the  formation  of  the  soluble  compound  (a  zin- 
cate) produced  when  zinc  hydroxide  is  dissolved  in  an 
aqueous  solution  of  an  alkali.  In  the  case  of  tartaric  acid, 
for  example,  it  will  be  found  that  the  ion  C^H^Og''  is  in 
combination  in  neutral  salts  of  that  acid,  while  the  ion 
C4H50g'  is  in  combination  in  acid  salts,  and  that  the  latter 
ion  may  be  employed  for  the  detection  of  the  potassium  ion. 

In  potassium  ferrocyanide  the  iron  cannot  be  detected  by 
the  usual  reactions  for  that  element,  because  in  this  com- 
pound the  iron  is  not  present  as  ferrous  ion,  but  as  a  ferro- 


10 

cyanogen  ion  ;  a  similarly  constituted  ion,  ferricyanogen  ion, 
is  also  present  in  potassium  ferricyanide :  these  complex  ions 
enter  unchanged  into  the  reactions  occurring  in  aqueous 
solutions.  Although  of  identical  composition,  they  yield 
different  reactions — for  example,  with  iron  salts :  the  ferro- 
cyanogen  ion  Fe(CN)g""  is  entirely  different  from  the  ferri- 
cyanogen ion  Fe(CN)g'''.  Similar  complex  ions  are  recog- 
nized as  existing  in  all  so-called  complex  salts :  in  the 
so-called  platinic  chloride,  or  more  correctly  hydrochlor- 
platinic  acid,  there  is  present  the  ion  PtClg"  in  combination 
with  2H' ;  this  ion  forms  with  two  potassium  ions  (2K')  the 
difficultly  soluble  salt  Kg*  PtClg",  potassium  chlorplatinate. 
Ammonia,  too,  forms  complex  ions  with  many  metals — for 
example,  Cu(NH3)4",  Zn(NH3)4**,  and  the  solubility  of 
argentic  chloride  in  ammonium  hydroxide  likewise  depends 
upon  the  formation  of  a  complex  ammonia  ion. 

The  electrolytic  dissociation  of  compounds  is  in  some 
cases  incomplete ;  as,  for  instance,  with  mercuric  chloride, 
HgClg.  Nevertheless,  the  total  quantity  of  chlorine  may  be 
precipitated  from  an  aqueous  solution  of  mercuric  chloride 
by  means  of  argentic  nitrate.     How,  then,  is  this  possible  ? 

Suppose  the  electrolytic  dissociation  of  a  salt  be  expressed 
— for  simplicity  using  potassium  chloride — by  the  equation  : 

KCI7 >K-4-CF 

(in  which  the  symbol  of  double  arrows  denotes  that  the 
reaction  is  reversible— i.  e.,  it  may  follow  the  direction  of 
either  arrow),  there  will  then  be  exhibited  for  this  trans- 
formation an  illustration  of  the  Law  of  Mass-action : 


c 


7 —  ^^  constant,  or  ,- 
o.c  '        b 

In  this  case  a  represents  the  number  of  undecomposed  mole- 
cules of  potassium    chloride ;  b,  the    number  of  potassium 


11 

cations;  and  c,  the  number  of  chlorine  anions.  Now,  the 
law  states  that  for  all  temperatures  the  relation  of  the  undis- 
sociated  portion  («)  to  the  dissociated  portions  (6,  c)  is  con- 
stant ;  there  is  always  a  definite  condition  of  equilibrium. 
If,  then,  a  solution  of  argentic  nitrate  is  added  to  a  solution 
of  potassium  chloride,  insoluble  argentic  chloride  is  formed, 
in  which  each  silver  ion  has  combined  with  a  chlorine  ion. 
Hence,  for  the  time  being,  the  status  of  equilibrium  corre- 
sponding to  the  foregoing  mass-action  equation    7 —  =  K, 

becomes  disturbed,  and  may  be  restored  only  on  condition 
that  new  ions  of  chlorine  (and  potassium)  be  dissociated 
from  the  potassium  chloride.  This  then  continually  occurs 
upon  further  addition  of  argentic  nitrate  until  practically  all 
of  the  potassium  chloride  is  dissociated  and  all  the  chlorine 
is  precipitated  as  argentic  chloride.  In  analogous  manner 
the  decomposition  proceeds  in  the  case  of  mercuric  chloride ; 
along  with  the  precipitation  of  the  dissociated  chlorine  ion 
by  the  silver  ion  disturbances  of  equilibrium  occur,  and  these 
must  be  continually  equalized  according  to  the  equation : 

HgCi,^— ±Hg-*+cr  +  cr, 

in  the  direction  of  the  upper  arrow  until  practically  all  of 
the  chlorine  is  precipitated  by  the  silver. 

Without  considering  here  similar  cases  (for  instance,  the 
precipitation  of  sulphides  by  means  of  hydrogen  sulphide), 
there  are  other  applications  of  the  law  of  mass-action  which 
may  be  discussed. 

In  the  precipitation  of  silver  by  chlorine,  or  chlorine  by 
silver,  advantage  is  taken  of  the  insolubility  of  argentic 
chloride.  However,  no  salt  is  wholly  insoluble,  and  even  in 
the  precipitation  of  argentic  chloride  the  clear  liquid  above 
the  precipitate  of  argentic  chloride  is  saturated  with  argentic 


12 

chloride ;  the  liquid  contains  dissolved  argentic  chloride 
together  with  chlorine  ions  and  silver  ions,  because  the  dis- 
solveil  argentic  chloride  is  partly  dissociated  : 

AgCl  =  Ag*-f  CI'. 

Here,  too,  the  equation  —  =:  K  holds  good.     If  the  concen- 
6.C 

tratiou  of  the  silver  ions  in  the  clear  liquid  above  the  pre- 
cipitate be  increased  by  the  addition  of  argentic  nitrate  solu- 
tion, b  is  increased ;  and  consequently,  since  - —  remains   con- 

b.c 

stant,  a  is  also  increased — that  is,  inasmuch  as  AgCl  is  only 
very  slightly  soluble  the  precipitation  is  rendered  more  com- 
plete. 

Therefore,  the  solubility  of  a  salt  may  be  diminished  by 
increasing  the  concentration  of  one  of  the  ions  of  the  salt  in 
the  solution — that  is,  by  the  addition  of  an  excess  of  the 
salt  wliich  produced  the  precipitate.  The  same  result  is 
achieved  in  the  precipitation  of  silver  by  means  of  hydro- 
chloric acid  when  an  excess  of  the  acid  is  employed,  thus 
increasing  the  amount  of  chlorine  ions  in  the  liquid. 

Again,  the  law  of  mass-action  comes  into  play  in  connec- 
tion, for  instance,  with  the  ferric  salts,  with  the  decompos- 
ing, hydrolytic  action  of  water.  The  neutral  ferric  salts  in 
aqueous  solution  are,  to  a  certain  extent,  separated  by  hydrol- 
ysis, as,  for  example  : 

FeCla  +  UOn- >FeC1.0H  -f  HCl ; 

Fe(C2H302)3+  2HOH7 >Fe(aH.O.)(OH),+  2UCJIfi,. 

Here,  again,  the  reaction,  as  indicated  by  the  double  arrows, 
being  reversible,  complete  decomposition  of  ferric  acetate 
may  be  practically  effected  in  the  direction  of  the  upper 
arrow  by  the  addition  of  water  and  warming  the  liquid — 
that  is,  all  of  the  iron  will  be  precipitated  as  basic  ferric 


13 

acetate.  Conversely,  in  the  direction  of  the  lower  arrow, 
the  reaction  occurs  in  cold  solutions  (and  also  by  the  addi- 
tion of  an  excess  of  acetic  acid).  In  this  case,  therefore,  the 
ferric  solution  employed  must  be  very  dilute  and  hot  in 
order  that  the  precipitation  shall  be  complete,  and  must  be 
filtered  while  hot,  so  that  the  precipitate  shall  not  redissolve 
in  the  liquid. 

In  this  category  also  belongs  the  precipitation  of  basic 
salts  from  solutions  of  antimony  and  bismuth. 

The  reaction  of  salts  depends  also,  under  certain  con- 
ditions, upon  hydrolysis.  Hydrogen  salts  (acids)  in  general 
have  an  acid  reaction  and  change  blue  litmus  to  red.  The 
intensity  of  the  reaction  depends  upon  the  strength  of  the 
acid — i,  e.y  the  amount  of  acid  which  separates  into  its  anion 
and  hydrogen,  the  reaction  being  due  to  the  hydrogen  ion. 
Hydroxyl  salts  (bases)  likewise  exhibit  stronger  or  weaker 
alkaline  reaction — i.  c,  they  change  red  litmus  to  blue,  the 
alkaline  reaction  being  due  to  the  hydroxyl  ion.  Neutral 
salts  in  general  have  no  reaction  upon  blue  or  red  litmus ;  if, 
however,  they  be  hydrolytically  separated,  the  reaction  of 
the  separated  portions  is  produced,  salts  of  the  strong  acids 
may  yield  an  acid  reaction,  and  salts  of  the  strong  bases  may 
yield  an  alkaline  reaction. 

The  transpositions  which  occur  in  reactions  may  be  ex- 
pressed by  equations.  They  may  be  written  to  represent  the 
transposition  of  ions,  as,  for  example : 

PtCV'  +  K-::=K2PtCl«; 
or  they  may  be  written  as  ordinary  aggregated  equations,  as, 
for  example  : 

H^PtClfi  +  2KC1  =  K^PtCle  +  2HC1. 
For  the  sake  of  simphcity,  and  in  conformity  with  previous 
editions,  the  aggregated  equations  will  be  retained  in  this 
edition. 


I.  PROPERTIES  OF  THE  BASES. 


FIRST   GROUP. 


Metals  precipitated  as  chlorides  by  HCl,  hydrochloric 
acid  :  Silver,  Mercury  (in  the  mercurous  condition),  and  Lead, 
(cations  Ag ',  Hg ',  and  Pb '). 

SILVER,  As  (ARGENTUM). 
Atomic  weight,  I07.93  (107.12);  valence,  1. 

White,  glittering  metal ;  specific  gravity,  10.57 ;  melting- 
point,  954°  C. 

AgNO^j  argentic  nitrate,  may  be  employed  in  making  the  tests, 

1.  HCl,  hydrochloric  acid,  or  a  soluble  chloride  precipitates 
white,  curdy  AgCl,  argentic  chloride.  At  first  the  liquid 
becomes  milky  in  appearance,  due  to  the  finely-divided  par- 
ticles of  precipitate  in  suspension,  but  on  shaking  or  heating 
the  liquid  the  precipitate  collects  in  curdy  masses  and  the 
liquid  becomes  clear. 

On  exposure  to  sunlight  the  precipitate  turns  violet  and 
finally  black,  due  to  the  liberation  of  a  slight  quantity  of 
chlorine.  The  precipitate  is  insoluble  in  HNO3,  nitric  acid, 
but  dissolv'CS  on  agitation  in  NH^OH,  ammonium  hydroxide, 
due  to  the  production  of  a  complex  argent-ammonia  cation, 
with  the  formation  of  argent-ammonium  chloride : 

AgCl  +  2NH,OH  -=  Ag(NH3)2Cl  +  2H2O, 
from  which  solution  it  may  be  reprecipitated  by  the  addition 

of  nitric  acid : 

15 


16 

Ag(NH3)2Cl  +  2HNO3  -  AgCl  +  2NH,N03. 
It  is  also  dissolved  by  KCN,  potassium  cyanide : 
AgCl  +  2KCN  =-  KAg(CN)2  -f-  KCl, 
and  in  the  absence  of  free  acid  by  'Nix.^S.fl.^j  sodium  hyposul- 
phite (thiosulphate). 

2.  NaOH,  sodium  hydroxide,  as  well  as  KOH,  potassium 
hydroxide,  precipitates  brownish-gray  Agfi,  argentic  oxide, 
insoluble  in  excess  of  either  reagent. 

3.  NH4OH,  ammonium  hydroxide  (very  dilute),  added  a 
drop  at  a  time,  precipitates  brownish-gray  AggO,  argentic 
oxide,  readily  soluble  in  a  slight  excess  of  the  reagent,  due  to  the 
production  of  the  complex  argent-ammonia  cation  Ag(NH3)2*, 
which  forms  Ag(NH3)20H,  argent-ammonium  hydroxide : 

AgP  +  4NH,0H  =  2Ag(NH3)pH  +  SHp. 

4.  HgS,  hydrogen  sulphide,  precipitates  black  AggS,  argen- 
tic sulphide,  insoluble  in  dilute  acids  and  in  (NH4)2S,  ammo- 
nium sulphide.  On  being  boiled  with  nitric  acid  the  precipi- 
tate dissolves,  with  the  formation  of  AgN03,  argentic  nitrate. 
Argentic  sulphide  is  also  soluble  in  potassium  cyanide  with 
the  formation  of  potassium  argentic  cyanide,  the  compound 
of  the  complex  anion  Ag(CN)2' : 

Ag2S  +  4KCN  =  2KAg(CN)2  +  K2S. 

5.  (NH4)2S,  ammonium  sulphide,  precipitates  black  AggS, 
argentic  sulphide,  insoluble  in  dilute  acids. 

6.  K2Cr04,  potassium  chromate,  produces  a  purplish-red. t 
precipitate  of  AggCrO^,  argentic  chromate,  soluble  in  am-' 
monium  hydroxide  and  in  nitric  acid. 

7.  NagHPO^,  sodium  hydrogen  phosphate,  precipitates 
yellowish,  flocculent  AgaPO^,  argentic  phosphate,  soluble  in 
ammonium  hydroxide  and  in  nitric  acid. 

8.  KI,  potassium  iodide,  precipitates  yellowish,  curdy  Agl, 
argentic  iodide,  insoluble  in  dilute  nitric  acid,  and  very 
sparingly  soluble  in  ammonium  hydroxide. 


17 

9.  KCN,  potassium  cyanide,  precipitates  white,  curdy 
AgCN,  argentic  cyanide,  soluble  in  excess  of  the  reagent 
and  in  ammonium  hydroxide,  insoluble  in  dilute  nitric  acid. 

10.  Compounds  of  silver  fused  with  ^3^003,  sodium  car- 
bonate, in  the  reducing  blowpipe  flame  on  charcoal  yield  a 
white,  ductile  globule  of  metallic  silver,  usually  without  an 
incrustation.  Occasionally  a  slight  reddish-brown  incrusta- 
tion of  argentic  oxide  is  produced  on  the  globule. 

MERCURY,   Hg  (HYDRARGYRUM). 
Atomic  weight,  200  (198.5) ;  valence,  I. 

Silver-white  metal ;  specific  gravity,  13.59 ;  solidifies  at 
—39.4°  C.  and  boils  at  357.2°  C. 

Mercury  forms  two  series  of  compounds,  named  respec- 
tively mercurous  and  mercuric  compounds.  HggO,  mercu- 
rous  oxide,  may  be  taken  as  the  type  of  the  mercurous,  and 
HgO,  mercuric  oxide,  as  the  type  of  the  mercuric  compounds. 

BEHAVIOR   OF   MERCURY   IN   THE  MERCUROUS  CONDITION. 

HgNO^y  mercurous  nitrate^  may  be  employed  in  making  the 
tests. 

1.  HCl,  hydrochloric  acid,  or  a  soluble  chloride  precipi- 
tates from  solutions  of  mercurous  salts  white  pulverulent 
HgCl,  mercurous  chloride  (calomel),  insoluble  in  water  and 
in  cold  dilute  acids,  easily  soluble  in  nitro-hydrochloric  acid 
(aqua  regia),  with  the  formation  of  HgClg,  mercuric  chloride 
(corrosive  sublimate)  : 

3HgCl  +  HNO,  +  3HC1  =  3HgCl,  -f  NO  +  2H2O. 
Ammonium  hydroxide  converts  the  HgCl,  mercurous  chlo- 
ride, into  black  NHgHggCl,  dimercurous  ammonium   chlo- 
ride, insoluble  in  excess  of  the  reagent : 

2HgCl  +  2NHPH  =  NH^Hg^Cl  +  NH.CI  +  2H2O. 

6  2* 


18 

2.  NaOH,  sodium  hydroxide,  or  KOH,  potassium  hy- 
droxide, precipitates  bh\ck  HggO,  mercurous  oxide,  insohible 
in  excess  of  the  reagent. 

3.  NH4OH,  ammonium  hydroxide,  produces  in  solutions 
of  mercurous  salts  a  black  precipitate  containing  nitrogen, 
depending  in  composition  npon  the  mercurous  salt  employed 
and  the  conditions  under  which  precipitation  has  occurred. 
For  example,  on  adding  ammonium  hydroxide  to  a  solution 
of  HgNOg,  mercurous  nitrate,  black  NH2Hg^,N03,  dimer- 
curous  ammonium  nitrate  (mercurius  solubilis  Hahnemanni), 
is  formed  : 

2HgN03  -f-  2NH4OH  =--  NH^Hg^NO,,  +  NH.NOs  +  2H2O. 
The  precipitate  is  insoluble  in  excess  of  the  reagent. 

4.  HgS,  hydrogen  sulphide,  as  well  as  (NH4)2S,  ammonium 
sulphide,  produces  a  black  precipitate,  consisting  of  a  mix- 
ture of  HgS,  mercuric  sulphide,  and  metallic  mercury  (not 
HggS,  mercurous  sulphide).  On  boiling  this  precipitate  with 
concentrated  nitric  acid,  a  white  compound  composed  of 
HgS,  mercuric  sulphide,  and  Hg(N03)2,  mercuric  nitrate 
[Hg3S2(N03)2],^^^  insoluble  in  nitric  acid,  is  formed,  while  the 
liquid  (filtrate)  contains  Hg(N03)2,  mercuric  nitrate.  Yellow 
ammonium  sulphide,  (NH4)2S^,  converts  the  mixture  of  HgS 
and  metallic  mercury  wholly  into  HgS,  mercuric  sulphide. 
Yellow  sodium  sulphide,  NagS^.,  as  well  as  yellow  potassium 
sulphide,  K2SJ,,  converts  the  mixture  into  HgS,  mercuric  sul- 
phide.    The  precipitate  is  soluble  in  nitro-hydrochloric  acid. 

5.  SnCl2,  stannous  chloride,^^^  added  in  very  small  quantity 
to  a  concentrated  solution  of  a  mercurous  salt,  precipitates, 
precisely  as  any  other  soluble  chloride,  white  HgCl,  mercu- 

S-HgNO, 

'  SnCl2,  stannous  chloride,  used  as  a  reagent,  always  contains  some  free 
HCl,  hydrochloric  acid. 


19 

rous  chloride.     When  SnClg  is  added  in  excess,  a  grayish 
precipitate  of  finely-divided  metallic  mercury  is  formed : 
SnCl^  -f  2HC1  +  2HgN03  =  Hg2  +  SnCl^  -f-  2HNO3. 

6.  KI,  potassium  iodide,  added  in  small  quantity  to  a 
solution  of  a  mercurous  salt,  precipitates  greenish  flocculent 
Hgl,  mercurous  iodide,  which  in  excess  of  the  reagent  dis- 
solves, with  the  separation  of  metallic  mercury  and  the  for- 
mation of  soluble  KaHgl^,  potassium  mercuric  iodide ; 
therefore,  when  much  potassium  iodide  is  added  to  a  dilute 
solution  of  a  mercurous  salt,  there  immediately  appears  a 
grayish  precipitate  of  metallic  mercury. 

7.  A  drop  or  two  of  a  solution  of  a  mercurous  salt  placed 
on  clean  copper  foil  produces  a  discoloration,  due  to  the  de- 
position of  metallic  mercury,  which  upon  being  gently  rubbed 
with  the  finger  becomes  silvery  white  and  mirror-like  in  ap- 
pearance. On  heating  the  foil  over  a  flame  the  deposit  dis- 
appears, due  to  the  volatilization  of  the  mercury. 

8.  Mercurous  salts  (with  the  exception  of  HgCl,  mercu- 
rous chloride,  which  volatilizes  unchanged),  when  heated  in  a 
small  dry  glass  reduction -tube  with  dry  Na2C03,  sodium  car- 
bonate, yield  a  sublimate  consisting  of  globules  of  metallic 
mercury. 

LEAD,   Pb  (PLUMBUM). 
Atomic  weight,  206.9  (205.35) ;  valence,  H. 

Bluish-white  metal ;  specific  gravity,  11.3;  melting-point, 
334°  C. 

Pb(C2H^02)2j  pluinbic  acetate  J  may  be  employed  in  making 
the  tests, 

1.  HCl,  hydrochloric  acid,  or  a  soluble  chloride  precipi- 
tates, iu  solutions  not  too  dilute,  white  flocculent  (sometimes 
crystalline)  PbC^,  plumbic  chloride;  soluble  at  12.5°  C.  in 


20 

135  parts  of  water,  and  at  the  boilinj^-point  in  30  parts  of 
water.  On  cooling  the  hot  saturated  aqueous  sohition,  the 
lead  salt  crystallizes  in  glistening  rhombic  needles.  It  is 
insoluble  in  ammonium  hydroxide;  soluble  with  difficulty 
in  dilute  acids;  easily  soluble  in  strong  hydrochloric  acid, 
particularly  on  heating. 

2.  NaOH,  sodium  hydroxide,  as  well  as  KOH,  potassium 
hydroxide,  precipitates  white,  flocculent  Pb(0H)2,  plumbic 
hydroxide  (mixed  with  a  slight  quantity  of  basic  lead  salt), 
— insoluble  in  ammonium  hydroxide;  slightly  soluble  in 
water ;  and  easily  soluble  in  excess  of  sodium  or  potassium 
hydroxide,  with  the  formation  of  NajPbO^,  sodium  plum- 
bite,^*^  or  KgPbOg,  potassium  plumbite  (as  a  sodium  or 
potassium  compound  of  the  anion  Pb02"). 

Pb(OH)2  +  2NaOH==  Na^PbO^  +  2H2O. 

3.  NH4OH,  ammonium  hydroxide,  precipitates  white,  floc- 
culent Pb(OH)2,  plumbic  hydroxide,  insoluble  in  excess  of 
the  reagent. 

4.  HgS,  hydrogen  sulphide,  or  (NH4)2S,  ammonium  sul- 
phide, precipitates  black  PbS,  plumbic  sulphide,  insoluble  in 
dilute  acids.  Boiling  nitric  acid  converts  it  into  Pb(N03)2, 
plumbic  nitrate ;  boiling  fuming  nitric  acid  oxidizes  it  to 
PbS04,  plumbic  sulphate,  which  is  slightly  soluble  in  nitric 
acid.  On  rapidly  passing  HgS,  hydrogen  sulphide,  into  a 
dilute  solution  of  lead  containing  free  hydrochloric  acid, 
cinnabar-red  PbgSClg,  plumbic  sulphochloride,^^^  is  often  pro- 
duced. By  the  further  addition  of  HgS,  the  plumbic  sulpho- 
chloride  is  converted  into  black  PbS : 

2PbCl2  +  H2S  =  Pb^SCl^  +  2HC1 ; 
Pb^SCl^  +  H^S  =  2PbS  -f-  2HC1. 


^0-Na.  ^Pb-01. 


21 

5.  KgCrO^,  potassium  chromate,  as  well  as  K2Cr207,  potas- 
sium dichromate,  precipitates  yellow  PbCrO^,  plumbic  chro- 
mate  (chrome-yellow),  insoluble  in  water  and  in  HC2H3O2, 
acetic  acid,  difficultly  soluble  in  nitric  acid,  easily  soluble  in 
sodium  or  potassium  hydroxide  : 

PbCrO,  +  4NaOH  =  Na2CrO,  +  Na2Pb02  +  2H2O. 

6.  H2SO4,  sulphuric  acid,  precipitates  white,  pulverulent 
PbS04,  plumbic  sulphate,  soluble  in  22,800  parts  of  pure 
water  at  ordinary  temperature,  less  soluble  in  water  containing 
sulphuric  acid,  more  soluble  in  the  presence  of  hydrochloric 
or  nitric  acid.  The  precipitate  is  soluble  in  warm  concentrated 
sulphuric  acid,  and  separates  on  diluting  the  solution  with 
water.  It  is  easily  soluble  in  NH4C2H3O2,  ammonium 
acetate,  and  in  the  presence  of  ammonium  hydroxide  in 
(NH4)2C4H40g,  neutral  ammonium  tartrate,  and  from  these 
solutions  the  lead  may  be  precipitated  by  K2Cr04,  potassium 
chromate,  as  yellow  PbCrO^,  plumbic  chromate. 

7.  KI,  potassium  iodide,  produces  in  solutions  not  too 
dilute  a  yellow,  pulverulent  precipitate  of  Pbl2,  plumbic 
iodide,  soluble  in  1235  parts  of  cold  water  and  in  194  parts 
of  boiling  water.  The  plumbic  iodide  separates  from  a  hot 
saturated  solution,  to  which  a  small  quantity  of  HC2H3O2, 
acetic  acid,  has  been  added,  in  glistening,  golden-yellow,  six- 
sided  plates. 

8.  Na2HP04,  sodium  hydrogen  phosphate,  precipitates 
white,  flocculent  Pb3(P04)2,  plumbic  phosphate,  soluble  in 
nitric  acid  and  in  sodium  hydroxide,  insoluble  in  acetic  acid. 

9.  Na2C03,  sodium  carbonate,  precipitates  in  cold  solutions 
neutral  PbCOg,  plumbic  carbonate,  and  in  boiling  solutions 
basic  carbonates,  in  which  (PbC03)2,Pb(OH)2  predominates, 
soluble  in  an  excess  of  the  reagent. 

10.  Compounds  of  lead  fused  witli  sodium  carbonate  in  the 
reducing  flame  on  charcoal  yield  a  white,  ductile  globe  of 


22 

metallic  lead  together  with  a  yellow  incrustation  of  PbO, 
plumbic  oxide. 

SECOND  GROUP. 

Metals  precipitated  from  acid  solutions  as  sulphides  by 
HgS,  hydrogen  sulphide  :  Mercury  (in  the  mercuric  condition), 
Copper,  Bismuth,  Arsenic,  Antimony,  Tin,  Cadmium,  Gold, 

and  Platinum,  (cations  Hg  "  ,  Cu  ",  Bi  *  * ',  As  "  *,  As , 

Sh"\  Sb ,  Sn",  Sn"\  Cd  *  *,  Au  *,  An*  *  *,  and  Pf  , 

Pt  •  •  • ',  and  the  anions  SnO/',  SnO/',  SnS,'^, ;  SbOg''',  SbO/'^ 
SbS/'',SbS/'';  AsO/,  ASO3'''  AsO/'',  AsS/'^  AsS/'')- 

The  sulphides  of  arsenic,  antimony,  and  tin  are  soluble  in 
alkaline  sulphides  with  the  formation  of  sulpho-salts.  These 
sulphides,  namely,  AS2S3,  AsgSg,  SbaSg,  Sb2S5,  and  SnSg,  enter 
into  combination  with  sulpho-bases ;  for  example,  ammonium 
sulphide,  to  form  soluble  sulpho-salts.  The  sulpho-salts  are 
combinations  of  sulphur-containing  anions  with  metallic 
ions. 

The  behavior  of  the  metals  when  heated  with  nitric  acid, 
and  the  formation  of  oxides,  are  described  under  the  heading 
"Dissolving  of  Metals  and  Alloys,"  page  127.  Tin  is 
soluble  in  hydrochloric  acid;  antimony  is  most  readily  dis- 
solved by  nitro-hydrochloric  acid. 

MERCURY,    Hg  (HYDRARGYRUM). 
Atomic  weight,  200  (198.5) ;   valence,  11. 

BEHAVIOR    OF     MERCURY     IN    THE    MERCURIC    CONDITION. 

HgCl2,  mercuric  chloride ^  or  Hg(^N0^2y  'i^i^i'curic  nitrate, 
may  he  employed  in  making  the  tests. 

1.  HgS,  hydrogen  sulphide,  and  also  (NHJgS,  ammonium 
sulphide,  produce  in  solutions  of  mercuric  salts  a  white  pre- 


23 

cipitate  of  Hg3S2Cl2^'>  or  Hg3S2(N03)2/'^  which,  on  the  further 
addition  of  the  reagent,  becomes  yellow,  then  brown,  and 
finally  is  converted  into  black  HgS,  mercuric  sulphide : 
3HgCl2  +  2H2S  =  Hg3S2Cl2  4-  4HC1 ; 
Hg3S2Cl2  +  H2S  =  3HgS  +  2HC1. 

HgS  is  not  dissolved  by  ammonium  sulphide ;  sometimes, 
however,  on  being  treated  with  ammonium  sulphide,  it  is 
converted  from  black  HgS  into  red  HgS  (cinnabar). 

NagS,  sodium  sulphide,  and  KgS,  potassium  sulphide  (par- 
ticularly in  the  presence  of  sodium  or  potassium  hydroxide), 
dissolve  mercuric  sulphide,  with  the  formation  of  Na2HgS2  ^^^ 
or  K2HgS2<'\  salts  of  the  anion  HgS2'0- 

Mercuric  sulphide  is  insoluble  in  boiling  hydrochloric  acid 
or  in  nitric  acid,  but  by  the  continued  action  of  hot  concen- 
trated nitric  acid  it  is  converted  into  the  white  insoluble 
double  salt  Hg3S2(N03)2  (as  in  the  case  of  HggS,  mercurous 
sulphide). 

Nitro-hydrochloric  acid  dissolves  mercuric  sulphide,  with 
the  formation  of  HgClg,  mercuric  chloride : 
3HgS  +  6HC1  +  2HNO3  =  3HgCl2  +  2NO  +  4H2O  +  S3. 

2.  NaOH,  sodium  hydroxide,  and  KOH,  potassium  hy- 
droxide, produce  a  brownish-red  precipitate  of  a  basic  salt, 
which,  upon  further  addition  of  the  reagent,  is  converted  into 
yellow  HgO,  mercuric  oxide.  As  mercuric  cyanide  is  not 
dissociated  in  aqueous  solution,  no  precipitate  is  produced 
when  NaOH  or  KOH  is  added  to  its  aqueous  solution. 

3.  NH4OH,  ammonium  hydroxide,  produces  a  white  pre- 
cipitate; thus,  in  a  solution  of  HgCl2  mercuric  chloride, 
white  NHgHgCl,  mercuric  ammonium  chloride,  is  produced : 

S_HgCl  S_HgNO, 

^^S-HgCl.  ^^S-HgNOj. 

»Hg<«^''  'Hg<^^ 


24 

HgCl^  +  2NH,OH  =  NH^HgCl  +  NH.Cl  +  2H2O. 

4.  SnCla,  stannous  chloride,  added  in  small  quantities  to 
mercuric  chloride  or  to  mercuric  salts  containing  a  very  slight 
quantity  of  free  hydrochloric  acid,  precipitates  white  HgCl, 
mercurous  chloride,  which,  on  the  addition  of  more  stannous 
chloride,  is  reduced  to  gray,  finely-divided,  metallic  mercury 
(very  delicate  reaction). 

5.  KI,  potassium  iodide,  precipitates  red  Hglg,  mercuric 
iodide,  soluble  in  excess  of  the  reagent,  with  the  formation 
of  K2Hgl4,  potassium  mercuric  iodide,  the  potassium  com- 
pound of  the  anion  Hgl/'. 

6.  A  drop  or  two  of  a  solution  of  a  mercuric  salt  placed 
on  clean  copper  foil  produces  a  discoloration,  due  to  the  depo- 
sition of  metallic  mercury,  as  in  the  case  of  mercurous  salts. 
On  gently  rubbing  the  spot  it  becomes  mirror-like  in  appear- 
ance, and  on  heating  the  foil  the  spot  disappears,  due  to  the 
volatilization  of  the  mercury. 

7.  Many  of  the  mercuric  salts,  when  heated  in  a  glass  re- 
duction-tube, sublime  undecomposed,  as,  for  example,  HgClg, 
mercuric  chloride  (corrosive  sublimate),  while  others  yield 
sublimates  which,  because  of  an  admixture  of  basic  salts,  are 
colored  yellow.  If  the  white  (or  yellow)  sublimate  be  covered 
with  dry  sodium  carbonate  and  again  heated,  red  mercuric 
oxide  is  produced,  which,  on  being  more  strongly  heated, 
breaks  up  into  metallic  mercury  and  oxygen. 

COPPER,   Cu  (CUPRUM). 
Atomic  weight,  63.6  (63.1 ) ;  valence,  I,  II. 

Reddish  metal ;  specific  gravity,  8.94  ;  melting-point,  1054° 
C. 

CuSO^y  cupric  sulphate,  may  be  employed  in  making  the  tests, 

1 .  HjS,  hydrogen  sulphide,  or  (NH4)2S,  ammonium  sulphide, 
precipitates  black  Cu8,  cupric  sulphide,  insoluble  in  dilute 


25 

acids,  insoluble  in  NagS,  sodium  sulphide,  and  in  KgS,  potas- 
sium sulphide.  Ammonium  sulphide  (particularly  the  yellow 
ammonium  sulphide)  dissolves  traces  of  the  precipitate,  with 
the  formation  of  Cu,Sj(NR,),=  {CuSU^}i,\S,.  Boiling 
nitric  acid  dissolves  CuS,  with  the  formation  of  Cu(N03)2, 
cupric  nitrate.  It  is  also  soluble  in  KCN,  potassium  cyanide, 
forming  the  potassium  compound  of  the  complex  ion  Cu(CN)2' : 
2CuS  +  4KCN  =  2KCu(CN)2  +  K^S^. 
The  precipitate  (CuS),  when  moist  and  exposed  to  the  air, 
readily  absorbs  oxygen,  with  the  formation  of  CuSO^,  cupric 
sulphate. 

2.  NaOH,  sodium  hydroxide,  or  KOH,  potassium  hy- 
droxide, produces  in  cold  solution  a  voluminous  flocculent 
precipitate  of  bluish- white  Cu(OH)2,  cupric  hydroxide,  insol- 
uble in  excess  of  the  reagent,  but  easily  soluble  in  ammonium 
hydroxide.  The  precipitate,  on  being  boiled  with  excess  of 
sodium  or  potassium  hydroxide,  loses  water  and  forms  black 
CuO,  cupric  oxide.  On  adding  sodium  or  potassium  hydrox- 
ide to  copper  solutions  containing  non-volatile  organic  acids, 
and  particularly  containing  such  organic  substances  as  glucose, 
(grape  sugar,)  glycerin,  etc.,  and  agitating  the  liquid,  the 
bluish-white  cupric  hydroxide  at  first  produced  is  immediately 
dissolved,  with  the  production  of  a  deep-blue  liquid.  ^'^ 

3.  NH4OH,  ammonium  hydroxide,  added  in  small  quanti- 
ties, produces  a  bluish-white  precipitate  of  a  basic  salt,  which 


^  This  property  is  made  use  of  in  the  preparation  of  an  alkaline  copper 
solution  in  which  cupric  sulphate  solution  is  added  to  a  strong  sodium 
hydroxide  solution  containing  KNaC^H^Og,  potassium  sodium  tartrate 
(Rochelle  salt),  the  whole  forming  a  deep-blue  liquid  (Fehling's  solution), 
which  is  employed  as  a  reagent  for  the  detection  of  glucose  (grape  sugar). 
On  boiling  Fehling's  solution  to  which  a  solution  containing  glucose  has 
been  added,  insoluble  red  Cu^O,  cuprous  f)xide,  or  yellow  CuOH,  cuprous 
hydroxide,  separates. 

B  3 


26 

is  soluble  in  an  excess  of  the  reagent,  producing  a  deep-blue  so- 
lution, due  to  the  formation  of  Cu(NH3)4S04,  cupric  ammonium 
sulphate,  a  compound  containing  the  complex  cupric  ammonia 
cation  Cu(NH3)4  *  *  (very  delicate  reaction).  Strongly  acid  solu- 
tions are  not  generally  precipitated  by  ammonium  hydroxide. 

4.  Na2HP04,  sodium  hydrogen  phosphate,  produces  a 
bluish-green,  flocculent  precipitate  of  Cu3(P04)2,  soluble  in 
ammonium  hydroxide. 

5.  K4Fe(CN)g,  potassium  ferrocyanide,  precipitates  brown- 
ish-red Cu2Fe(CN)g,  cupric  ferrocyanide  (very  delicate  reac- 
tion). 

6.  KCN,  potassium  cyanide,  added  in  excess  to  a  neutral 
or  ammoniacal  solution  of  a  salt  of  copper,  produces  a  color- 
less solution  of  KCu(CN)2,  potassium  cuprous  cyanide : 

Cu(N03)2  +  2KCN  -  Cu(CN)2  +  2KNO3; 
2Cu(CN)2  +  2KCN  =  2KCu(CN)2  +  2CN. 
The  copper  of  this    potassium  salt  of  hydrocuprocyanic 
acid^'^  is  not  precipitated  by  hydrogen  sulphide  (correspond- 
ing to  the  iron  in  potassium  ferro-  and  ferricyanide,  which  is 
not  precipitated  by  the  ordinary  reagents). 

7.  KI,  potassium  iodide,  produces  in  solutions  to  which 
ferrous  sulphate  has  been  added  a  white  precipitate  of  Cul, 
cuprous  iodide  (a  compound  of  the  cation  Cu ' ) : 

2CUSO4  +  2FeS04+  2KI  -=  2CuI  +  Fe,{80,),  -f  K^SO^. 

8.  KCNS,  potassium  sulphocyanide,  followed  by  the  addi- 
tion of  H2SO3,  sulphurous  acid,  produces  a  white  precipitate 
of  CuCNS,  cuprous  sulphocyanide: 

2CUSO4  -h  2KCNS  +  H2SO3  4  H2O  =  2CuCNS  +  K^SO^  + 

2H2SO4. 


'  HCu(CN)„  the  complex  cupro-cyanogen  anion  Cu(CN)''2  in  combi- 
nation with  the  cation  H ' . 


27 

9.  A  bright  piece  of  iron  (knife-blade)  free  from  grease 
placed  in  a  solution  of  copper  is  soon  covered  with  a  reddish 
deposit  of  metallic  copper. 

10.  Compounds  of  copper  mixed  with  sodium  carbonate 
and  strongly  heated  on  charcoal  in  the  reducing  flame  yield 
reddish  spangles  or  globules  of  metallic  copper. 

11.  Compounds  of  copper  fused  in  a  bead  of  borax,  ^326^07, 
held  in  a  loop  of  platinum  wire  in  the  oxidizing  flame  of  the 
blowpipe,  yield  a  bluish-green  bead.  Fused  in  a  bead  of 
sodium  ammonium  ])hosphate,  NaNH^HPO^  (microcosmic 
salt),  they  yield,  in  the  oxidizing  flame,  a  bluish-green  bead, 
which,  when  heated  in  the  reducing  flame,  becomes  reddish 
brown  and  opaque,  due  to  the  presence  of  separated  metallic 
copper.  The  addition  to  the  bead  of  a  little  metallic  tin 
facilitates  the  reduction. 

BISMUTH,  Bi. 
Atomic  weight,  208.5  (206.9) ;  valence.  III. 

Reddish-white  metal ;  specific  gravity,  9.82  ;  melting-point, 
270°  C. 

Bi(NO^)^  or  BiCl^  may  he  employed  in  making  the  tests. 

1.  HgS,  hydrogen  sulphide,  or  (^114)28,  ammonium  sul- 
phide, precipitates  brownish-black  BigSg,  bismuth  sulphide, 
insoluble  in  dilute  acids  and  in  ammonium  sulphide.  It  is 
dissolved  by  boiling  nitric  acid,  forming  Bi(N03)3,  bismuth 
nitrate. 

2.  NaOH,  sodium  hydroxide,  KOH,  potassium  hydroxide, 
or  NH4OH,  ammonium  hydroxide,  precipitates  white,  amor- 
phous BiO-OH,  bismuth  hydroxide,  insoluble  in  excess  of 
the  reagent. 

3.  KgCrO^,  potassium  chromate,  precipitates  yellow,  crys- 
talline (BiO)2Cr04,  basic  bismuth  chromate,  insoluble  in 
sodium  hydroxide,  soluble  in  nitric  acid. 


28 

4.  A  clear  solution  of  a  bismuth  salt,  when  poured  into  a 
large  quantity  of  water  (provided  the  bismuth  solution  does  not 
contain  too  much  free  acid),  produces  a  milky  turbidity,  due 
to  the  separation  of  a  white  basic  salt  of  bismuth.  BiClg,  bis- 
muth chloride,  yields  BiOCl,  bismuth  oxychloride.  Bi(N03)3, 
bismuth  nitrate,  yields  first  BiONOg,  bismuth  oxynitrate,  and 
afterward,  especially  on  heating  the  liquid,  (BiO)2N030H/*^ 
A  few  drops  of  hydrochloric  acid  or  of  NH^Cl,  ammonium 
chloride,  added  to  a  bismuth  nitrate  solution  before  it  is 
poured  into  the  water,  cause  the  separation  of  the  bismuth 
as  BiOCl,  bismuth  oxychloride.  The  reaction  with  Bids  is 
the  more  delicate.  Tartaric  acid  does  not  interfere  with  this 
reaction. 

5.  SnClg,  stannous  chloride,  dissolved  in  a  solution  of 
sodium  hydroxide,  produces  a  black  precipitate  of  BiO,  bis- 
muth oxide : 

2Bi(N03)3  +  Na2Sn02  +  6NaOH  =  2BiO  -f  Na^SnOg  + 
6NaN03  +  3H2O. 

6.  Bismuth  salts,  mixed  with  sodium  carbonate  and  heated 
in  the  reducing  flame  on  charcoal,  yield  brittle  globules  of  me- 
tallic bismuth  and  a  yellow  incrustation  of  BigOg,  bismuthous 
oxide. 

ARSENIC,  As   (ARSENICUM). 
Atomic  weight,  75. 0  (74-. 4)  ;   valence,  III,  V. 

Steel-gray  non-metal;  specific  gravity,  5.72  at  14°  C. 

Arsenic  forms  two  compounds  with  oxygen, — AS2O3,  arsen- 
ious  oxide  or  anhydride,  and  AS2O5,  arsenic  oxide  or  anhy- 
dride. 


1  Bi— O— NOo 
II 
Bi— O— OH. 


29 

BEHAVIOR   OF    ARSENIC    IN    THE    ARSENIOU6    CONDITION, — 
AS   ARSENIOUS   ACID. 

As^O^,  arsenious  oodde,  which,  when  dissolved  in  water ,  forms 
H^AsO^,  arsenious  add,  may  be  employed  in  making  the-  tests. 

1.  HgS,  hydrogen  sulphide,  precipitates,  from  warm  solu- 
tions acidulated  with  hydrochloric  acid,  yellow  AsgSg,  arseni- 
ous sulphide,  which  is  soluble  in  ammonium  sulphide  and  in 
(NH4)2C03,  ammonium  carbonate,  but  is  insoluble  in  hydro- 
chloric acid.  Dissolved  in  ordinary  colorless  ammonium 
sulphide  it  forms  (NHJ3ASS3,  ammonium  sulpharsenite,  a 
compound  of  the  anion  AsSg'^',  and  from  this  solution  it 
may  be  reprecipitated  by  acids  as  AS2S3,  arsenious  sulphide : 

2(NH,)3AsS3  +  6HC1  =  As^S,  +  6NH,C1  +  3H2S. 
Dissolved  in  yellow  ammonium  sulphide  it  forms  (NH4)3AsS4, 
ammonium  sulpharseniate,  a  compound  of  the  anion  AsS^'''. 
From  this  solution    it   is    precipitated   by    acids   as   AS2S5, 
arsenic  sulphide : 

AS2S3  +  3(NH,)2S  -+82  =  2(NH,)3AsS4 ; 

2(NH4)3AsS,  +  6HC1  =  AS2S5  +  GNH^Cl  +  3H2S. 
Ammonium  carbonate  dissolves  AS2S3  with  the  formation 
of   ammonium    sulpharsenite   and   ammonium   arsenite,  the 
latter  being  a  compound  containing  the  anion  AsOg' : 
,   AS2S3  +  2(NH4)2C03  =  (NH,)3AsS3  +  NH4ASO2  +  2CO2. 
Acids  reprecipitate  it  from  this  solution  as  AS2S3 : 
(NH,)3AsS3  +  NH,As02  +  4HC1  =  AS2S3  +  4NH,C1  + 

2H2O. 
AS2S5,  arsenic  sulphide,  dissolved  in  ammonium  carbonate 
forms  ammonium   sulpharseniate  and    ammonium  arseniate, 
the  latter  being  a  compound  containing  the  anion  AsO^''',  or 
HAsO/'  : 

4AS2S5  +  12(NH,)2C03  +  3H2O  -  5(NH,)3AsS,  + 
3(NH,)2HAsO,  +  3NH,HC03  -f-  9CO2. 


30 

From  this  solution  acids  reprecipitate  it  as  AS2S5 : 
5(NH,)3AsS,  +  3(NH,)2HAsO,   +    21HC1  -  4AS2S5  -f 
21NH,C1  +  12Hp. 

2.  AgNOa,  argentic  nitrate,  added  to  an  aqueous  solution 
of  arsenious  acid  and  very  dilute  ammonium  hydroxide 
added  drop  by  drop  produces  a  yellow  curdy  precipitate  of 
Ag3As03,  argentic  arsenite,  soluble  in  nitric  acid  with  the 
formation  of  arsenious  acid  and  argentic  nitrate,  and  in  am- 
monium hydroxide  with  the  formation  of  complex  argentic 
ammonia  compounds. 

3.  CuSO^,  cupric  sulphate,  added  to  an  aqueous  solution 
of  arsenious  acid,  and  very  dilute  ammonium  hydroxide 
subsequently  added  drop  by  drop,  produces  a  greenish  floc- 
culent  precipitate  of  CuHAsOg,  cupric  arsenite  (Scheele's 
green),  soluble  in  excess  of  ammonium  hydroxide  and  in  acids. 
If,  however,  sodium  hydroxide,  or  potassium  hydroxide  in 
excess,  instead  of  ammonium  hydroxide,  be  added  to  the 
solution  of  arsenious  acid,  followed  by  the  addition  of  a  few 
drops  of  dilute  cupric  sulphate  solution,  a  blue  solution  is 
produced  from  which  on  being  heated  reddish-brown  CugO, 
cuprous  oxide,  will  separate : 

NaaAsOa  +  2CuSO,  +  4NaOH  =  Cu^O  +  NaaAsO, 
+  2Na2SO,  -h  2H2O. 
(Distinction  from  arsenic  acid.     The  anion  AsOg'''  is  con- 
verted into  the  anion  AsO^'".) 

4.  Marshes  Test. — When  a  few  drops  of  a  solution  of  ar- 
senious acid  or  a  soluble  arsenite  are  placed  in  an  apparatus 
in  which  hydrogen  is  being  evolved,  the  nascent  hydrogen 
reduces  the  arsenical  compound,  and  gaseous  AsHg,  hydrogen 
arsenide  (arsenuretted  hydrogen),  is  evolved  with  the  free 
hydrogen : 

H3ASO3  +  3Zn  -f  3H2SO4  =  AsHg  -f  3ZnSO,  +  3H2O. 
When  this  mixture  of  hydrogen  and  hydrogen  arsenide  is 


31 

slowly  passed  through  a  glass  tulxi  heated  to  incipicDt  red- 
ness, the  hydrogen  arsenide  is  decomposed,  and  the  arsenic  is 
deposited  in  the  metallic  state  on  the  inner  surface  of  the 
tube  just  beyond  the  heated  part,  as  a  lustrous  brown,  gray, 
or  black  coating.  For  this  purpose  the  apparatus  of  Marsh, 
Fig.  1,  is  best  adapted. 

Fig.  1. 


The  apparatus  consists  of  a  small  generating  flask.  A,  a 
drying-tube,  By^^^  containing  small  pieces  of  calcium  chlo- 
ride, and  a  reduction-tube,  (7,  of  hard  glass,  contracted  at 
intervals. 

The  metallic  zinc  and  concentrated  sulphuric  acid  (diluted 
with  about  four  volumes  of  water)  used  in  the  operation 
must  be  free  from  arsenic,  and  therefore  the  following  con- 
trol test  should  always  be  made  to  determine  their  purity. 
Zinc  is  placed  in  the  flask  A,  and  the  drying-tube  By  to- 
gether with  the  reduction-tube  C,  is  connected  with  the 
flask.  Dilute  sulphuric  acid  (1-4)  is  introduced  through  the 
funnel-tube  until  the  zinc  is  covered.  When,  after  some 
minutes,^^^  the  evolved  hydrogen  has  expelled  the  air  from  the 


*  The  drying-tube  is  sometimes  dispensed  with,  and  the  reduction-tube 
connected  directly  with  the  delivery-tube  of  the  flask. 

^  If  the  action  is  slow,  as  is  usually  the  case  when  pure  zinc  is  em- 
ployed, it  may  be  accelerated  by  the  addition  of  a  few  drops  of  platinic 
chloride.  Some  observers,  however,  state  that  traces  of  arsenic  may  be 
retained  by  the  precipitated  platinum. 


32 

entire  apparatus/*^  the  flame  of  a  Bunsen  burner  is  applied  to 
that  part  (at  D)  of  the  reduction-tube  l^etvveen  the  contracted 
portion  and  the  drying-tube,  and  the  tube  then  heated  to 
'incipient  redness.  After  the  flame  has  been  applied  for  sev- 
eral minutes,  the  contracted  i)art  of  the  reduction-tube  is  ex- 
amined for  the  presence  of  a  brownish,  gray,  or  black  lus- 
trous deposit.  Should  such  a  de[)osit  be  found,  it  indicates 
that  either  the  zinc  or  the  sulphuric  acid,  or  both,  are  con- 
taminated with  arsenic  and  therefore  unfit  for  use  in  the  test. 

If  no  deposit  is  produced  by  the  above  test,  the  application 
of  the  heat  is  continued,  and  the  solution  containing  arsenic 
is  introduced  into  the  flask,  through  the  funnel-tube.  After 
the  lapse  of  some  minutes  the  contracted  part  of  the  tube 
immediately  beyond  the  flame  is  examined  for  the  presence 
of  a  brownish,  gray,  or  black  deposit.^^^  A  deposit  having 
formed,  the  reduction-tube  is  detached  (leaving  it  open  at 
both  ends,  to  permit  the  free  access  of  air),  inclined  over  a 
small  flame,  and  gently  heated  at  the  part  containing  the 
deposit.  The  arsenic  volatilizes,  combines  with  oxygen,  and 
deposits  beyond  the  part  heated,  as  AsgOg,  arsenious  oxide,  in 
minute  octahedral  crystals.^^^ 

1^  the  gas  is  ignited  as  it  escapes  from  the  contracted  end 
of  the  tube,  and  the  temperature  of  the  flame  is  reduced  by 
holding  a  piece  of  cold  porcelain  in  it,  incomplete  combustion 

'  Unless  the  air  is  expelled,  an  explosion,  which  may  cause  pei-sonal 
injury,  is  likely  to  occur  when  the  flame  is  applied  to  the  reduction- 
tube. 

2  Antimony  yields  a  deposit  much  resembling  in  color  tliat  produced 
by  arsenic.  The  arsenical  deposit  is  soluble  in  fresh  NaOCl,  sodium 
hypochlorite,  whereas  the  antimony  deposit  is  insoluble  in  that  reagent. 

^  The  antimony  deposit  volatilizes  and  yields  a  white  sublimate,  which 
is  generally  amorphous,  or  consists  of  minute  granules  and  opaque  gran- 
ular masses;  but  it  may  occasionally  contain  a  very  small  number  of 
well-defined  octahedral  crystals  of  Sb^Oj,  antinH.nious  oxide. 


33 

occurs,  and  the  arsenic  is  deposited  on  the  porcelain  in  the 
metallic  state  in  lustrous  brown,  gray,  or  black  spots : 

2ASH3  4-  O3  ==  As2  +  3H2O. 
The  arsenical  deposit  is  soluble  in  fresh  NaClO,  sodium  hy- 
pochlorite.    (Distinction  from  antimony.) 

As2  +  3NaOCl  +  3H2O  =  2H3ASO3  +  3NaCl. 

As  hydrogen  arsenide  is  exceedingly  poisonous,  it  should 
not  be  allowed  to  escape  in  the  room,  but  should  be  decom- 
posed by  igniting  it  as  it  escapes  from  the  tube,  or  conducting 
it  into  a  solution  of  argentic  nitmte,  whereby  reduction  of  the 
silver  salt  occurs  with  the  separation  of  metallic  silver,  the 
arsenic  remaining  in  solution  : 

AsHg  +  6 AgN03  4-  SU.O  =  6Ag  -f  H3ASO3  +  6HNO3. 

5.  Beinsch's  Test. — Metallic  copper  reduces  arsenious  oxide 
in  acid  solution  to  metallic  arsenic,  which  is  deposited  on  the 
copper  as  CugAsg,  cupric  arsenide.  The  arsenical  solution  is 
acidulated  with  about  one-seventh  of  its  volume  of  hydro- 
chloric acid,  a  clean  piece  of  copper  foil  placed  in  the  solution, 
and  the  whole  heated  and  kept  almost  at  the  boiling-point 
for  several  minutes.  In  this  hot  solution  the  arsenic  is 
deposited  on  the  foil  as  a  grayish  or  black  coating.  The  foil 
is  taken  from  the  liquid  and  im- 
mersed several  times  in  water  to 
wash  oif  the  hydrochloric  acid, 
then  pressed  (without  rubbing) 
between  filter  paper  to  free  it  from 
adherent  moisture,  and  finally 
completely  dried  by  being  heated 
in  a  porcelain  dish  on  a  water- 
bath.      It    is    then   placed    in   a 

reduction-tube  near  the  contracted  part,  the  tube  inclined, 
and  the  part  containing  the  foil  gently  heated  over  a  small 
flame  (Fig.  2). 


34 

Volatilization  of  the  arsenic  and  combination  with  oxygen 
take  place,  and  octahedral  crystals  of  AsgOg,  arsenious  oxide, 
are  deposited  in  the  cooler  part  of  the  tube. 

6.  Arsenious  oxide  heated  in  a  reduction-tube  sublimes 
unchanged,  and  is  deposited  in  the  cooler  portion  of  the  tube 
in  octahedi-al  crystals.  Heated  in  a  dry  reduction-tube  with 
charcoal,  a  grayish  or  black  mirror-like  deposit  of  metallic 
arsenic  is  formed  in  the  cooler  part  of  the  tube : 

AsA  +  Q^^As^  +  SCO. 

7.  Arsenious  oxide  or  compounds  of  arsenic  heated  on 
charcoal  in  the  reducing  flame  produce  a  garlic-like  odor. 
(The  arsenious  oxide  is  first  reduced  to  metallic  arsenic,  which 
volatilizes  and  combines  with  oxygen  to  form  AS2O3,  which 
sometimes  collects  as  an  incrustation  on  the  charcoal.) 

8.  Arsenious  oxide  or  an  arsenite,  mixed  with  six  times  its 
bulk  of  a  dry  mixture  consisting  of  equal  parts  of  sodium 
carbonate  and  potassium  cyanide  and  heated  in  a  reduction- 
tube,  is  reduced,  with  the  formation  of  a  ])lack  glistening 
sublimate  of  metallic  arsenic  in  the  cool  part  of  the  tube : 

AsPs  +  3KCN  =  As,  +  3KCNO. 

BEHAVIOR   OF    ARSENIC    IN    THE    ARSENIC    CONDITION, — AS 
ARSENIC  ACID. 

AS2O5,  arsenic  oxide,  which  forms  H^AsO^,  arsenic  acidy 
when  dissolved  in  water,  or  Na^AsO^,  sodium  arseniate,  may 
be  employed  in  making  the  tests. 

1.  HgS,  hydrogen  sulphide,  conducted  into  the  solution 
does  not  at  first  produce  a  precipitate  in  cold  solutions,  but 
reduces  the  arsenic  acid  to  arsenious  acid.  Heating  the  solu- 
tion facilitates  the  reduction  : 

H3ASO,  -f  H^S  =  H3ASO.,  -I-  HP  -[-  S. 
Continuing  the  addition  of  hydrogen  sulphide,  AS2S3,  arsen- 
ious sulphide,  is  precipitated  : 

2H3ASO3  +  3H2S  =  AS2S3  -j-  6H2O. 


35 

The  final  precipitate  is  therefore  a  mixture  of  arsenious  sul- 
phide and  sulphur  (AS2S3  +  S). 

If  the  acidulated  arsenic  acid  solution  be  heated  to  70°  C. 
and  hydrogen  sulphide  be  conducted  into  the  solution,  yellow 
AsgSg,  arsenic  sulphide,  will  at  once  be  precipitated. 

2.  AgNOg,  argentic  nitrate,  added  to  a  solution  of  arsenic 
acid  which  has  been  exactly  neutralized  with  ammonium 
hydroxide,  or  to  an  arseniate,  precipitates  reddish-brown 
AggAsO^,  argentic  arseniate,  soluble  in  nitric  acid  and  in 
ammonium  hydroxide : 

H3ASO,  +  3AgN03  -h  3NH,OH  =  AggAsO,  +  3NH,N03 
-f  3H2O. 

3.  CUSO4,  cupric  sulphate,  added  to  a  solution  of  arsenic 
acid,  followed  by  the  addition  of  ammonium  hydroxide  drop 
by  drop,  or  to  an  arseniate,  produces  a  bluish-green  precipi- 
tate of  CuHAs04,  cupric  arseniate,  soluble  in  an  excess  of 
ammonium  hydroxide  and  in  acids. 

4.  The  behavior  of  arsenic  acid  in  Marsh's  test  or  Reinsch's 
test,  in  the  reduction-tube,  mixed  with  charcoal,  and  on  char- 
coal itself  is  identical  with  arsenious  acid. 

5.  MgSO^,  magnesium  sulphate,  added  to  a  solution  of  ar- 
senic acid  or  an  arseniate,  followed  by  the  addition  of  NH4CI, 
ammonium  chloride,^^^  and  ammonium  hydroxide  (magnesia 
mixture),  precipitates  white,  crystalline  MgNH4As04  +  6H2O, 
ammonium  magnesium  arseniate : 

H3ASO4  -h  MgSO^  +  3NH4OH  =  MgNH^AsO^  +  (NH4)2S04 

-f  3H2O. 
In  concentrated  solutions  the  precipitate  forms  immediately, 
and  in  dilute  solutions  gradually ;  but  is  always  perceptibly 
crystalline.     It  is  soluble  in  15,293  parts  of  cold  water  and 

1  The  addition  of  ammoniuin  chloride  is  for  the  purpose  of  preventing 
the  precipitation  of  magnesium  hydroxide. 


36 

less  soluble  in  water  containing  ammonium  hydroxide ;  easily 
soluble  in  dilute  acids,  from  which  solutions  it  is  reprecipitated 
by  the  addition  of  ammonium  hydroxide. 

6.  NH4HM0O4,  ammonium  molybdate,  added  to  a  solution 
of  ai'senic  acid  rather  strongly  acidulated  with  nitric  acid, 
and  the  whole  gently  warmed,  produces  a  yellow  i)recipitatc 
of,  possibly,  (NH4)3As04(Mo03)i2,  ammonium  molybdoarseni- 
ate,  soluble  in  ammonium  hydroxide  and  reprecipitated  from 
this  solution  by  nitric  acid.  The  ])resence  of  hydrochloric 
acid  or  of  chlorides  interferes  with  the  delicacy  of  the  reaction. 

7.  KI,  potassium  iodide,  added  to  a  solution  of  arsenic 
acid  acidulated  with  hydrochloric  acid,  is  decomposed  with 
the  liberation  of  free  iodine : 

H3ASO,  +  2KI  +  2HC1  =-  21  -h  H3ASO3  f  2KC1  +  H^O. 
On  agitating  the  liquid  with  carbon  disulphide  or  with  chlo- 
roform the  iodine  will  be  extracted,  imparting  a  pinkish- 
violet  color  to  the  carbon  disulphide  or  chloroform. 

8.  To  detect  arsenic  acid  in  the  presence  of  arsenious  acid 
(providing  the  compounds  are  soluble  in  water)  their  behavior 
with  magnesia  mixture  (compare  above,  5)  is  made  use  of; 
arsenious  acid  produces  no  precipitate  with  magnesia  mixture. 
In  case  the  compound  is  insoluble  in  water,  it  is  dissolved  in 
hydrochloric  acid,  and  the  arsenious  acid  is  precipitated  in 
cold  solution  with  hydrogen  sulphide.  The  resulting  arseni- 
ous sulphide  is  removed  by  filtration,  the  filtrate  is  warmed, 
and  hydrogen  sulphide  again  conducted  into  the  liquid.  The 
production  of  a  precipitate  indicates  the  presence  of  arsenic 
acid. 

ANTIMONY,  Sb  (STIBIUM). 
Atomic  weight,  120.2  (119.3) ;  valence,  III,  V. 

Silvery- white  metal ;  specific  gravity  6.7  ;  melting-point, 
425°  C. 


37 

Antimony  forms  two  typical  compounds  with  oxygen, — 
Sb203,  antimonious  oxide,  and  SbgO^,  antimonic  oxide. 

BEHAVIOR  OF  ANTIMONY  IN  THE  ANTIMONIOUS  CX)NDITION. 

SbCl.^,  antimonious  chloride,  may  be  employed  in  making  the 


1 .  HgS,  hydrogen  sulphide,  produces  in  solutions  of  anti- 
monious salts  which  are  not  too  strongly  acidulated  an  omnge- 
red  precipitate  of  Sb2S3,  antimonious  sulphide,  insoluble  in 
dilute  acids,  soluble  in  concentrated  hydrochloric  acid  (without 
the  separation  of  sulphur)  and  also  in  ammonium  sulphide 
and  in  sodium  or  potassium  sulphide;  insoluble  in  ammonium 
carbonate  (distinction  from  arsenic).  When  dissolved  in 
colorless  ammonium  sulphide  it  forms  (NH4)3SbS3,  ammonium 
sulphantimonite,  a  compound  of  the  anion  SbSa"' : 

Sb^Sg  +  3(NH,)2S  ==  2(NH,)3SbS3 ; 
and  when  dissolved  in  yellow  ammonium  sulphide  it  forms 
(NH^)3SbS4,  ammonium  sulphantimonate,  a  compound  of  the 
anion  SbS/^' : 

Sb^Sj  +  3(NH,)2S  +  82  =  2(NH,)3SbS,. 
Hydrochloric  acid  precipitates  from  the  sulphantimonite  so- 
lution Sb2S3,  and  from  the  sulphantimonate  solution  SbgS^ : 
2(NH,)3SbS3  +  6HC1  =  Sb2S3  +  6NH,C1  +  3H2S ; 
2(NH4)3SbS,  +  6HC1  =  ^\^,  +  6NH,C1  +  3H2S. 

2.  NaOH,  sodium  hydroxide,  as  well  as  KOH,  potassium 
hydroxide,  produces  a  white  voluminous  precipitate  of 
SbO-OH,  antimonious  hydroxide,  readily  soluble  in  an  ex- 
cess of  the  reagent,  forming  NaSbOg,  sodium  antimonite,  or 
KSb02,  potassium  antimonite,  compounds  of  the  anion 
Sb02'.  On  being  boiled  in  the  alkaline  liquid  the  pre- 
cipitate of  SbO-OH  is  converted  into  Sb203,  antimonious 
oxide. 

3.  NH4OH,    ammonium    hydroxide,    precipitates    white 

4 


38 

SbO-OH,  antirnonious    hydroxide,   insoluble    in    an    excess 
of  the  reagent.     Tartaric  acid  prevents  the  precipitation. 

4.  On  pouring  a  solution  of  an  antirnonious  salt,  as,  for 
example,  SbClg,  antirnonious  chloride,  into  a  large  quantity 
of  water,  a  white  precipitate  of  a  mixture  of  SbOCl,  anti- 
rnonious oxychloride,  and  Sb405Cl2  is  produced : 

SbClg  +  HP  =  SbOCl  +  2HC1 ; 

4SbCl3  +  5H2O  =  SbAClz  +  lOHCl. 
A  milkiness  is  produced  in  water  by  even  the  slightest  quan- 
tity of  antirnonious  chloride.     Tartaric  acid  prevents  the  pre- 
cipitation by  dissolving  the  precipitate  with  the  formation  of 
a  complex  compound  : 

SbOCl  +  H^C.HA  =  (SbO)HC4HA  +  HCl. 

5.  Soluble  salts  of  antimony,  placed  in  a  flask  in  which 
hydrogen  is  being  generated  from  zinc  and  dilute  sulphuric 
acid  (1-4),  are  decomposed,  with  the  formation  of  gaseous 
SbHg,  antimonious  hydride  (antimonuretted  hydrogen) : 

2SbCl3  +  Zufi  +  3H2SO4  =  2SbH3  +  3ZnCl2  +  SZnSO^. 
The  apparatus  of  Marsh  is  best  adapted  for  this  purpose,  and 
the  same  precautions  as  given  under  arsenic  should  be  ob- 
served.    (See  page  31 .) 

On  heating  the  reduction-tube  of  Marsh's  apparatus  to 
dull  redness  and  slowly  passing  antimonious  hydride  through 
the  tube,  the  compound  is  reduced,  and  a  lustrous  brown 
or  black  deposit  of  metallic  antimony  is  formed  in  the  part 
of  the  tube  before  the  flame,  or  on  both  sides  of  the  flame. 
If  the  gas  be  ignited  as  it  escapes  from  the  contracted  end  of 
the  tube  and  the  temperature  of  the  flame  reduced  by  holding 
a  piece  of  cold  porcelain  in  it,  incomplete  combustion  will 
occur,  and  the  antimony  will  be  deposited  on  the  porcelain 
in  dull  brownish  or  black  spots : 

2SbH3-hO,=-Sb2+3H20. 


39 

The  deposit  of  metallic  antimony  is  insoluble  in  fresh  sodium 
hypochlorite  (distinction  from  arsenic). 

The  deposit  of  metallic  antimony  in  the  tube,  on  being 
gently  heated  over  a  small  flame  with  free  access  of  air/^^  vol- 
atilizes, combines  with  oxygen,  and  condenses  in  the  cooler 
part  of  the  tube  as  white  SbjOg,  antimonious  oxide.  The 
sublimate  is  usually  entirely  amorphous,  but  occasionally 
may  contain  octahedral  crystals  of  antimonious  oxide. 

6.  Compounds  of  antimony  in  acid  solution  are  reduced 
on  being  heated  with  a  piece  of  bright  copper  foil,  with  the 
deposition  of  the  antimony  as  a  grayish  or  black  coating 
upon  the  copper.  On  washing  the  foil  with  water,  drying, 
and  gently  heating  it  in  a  small  reduction-tube  over  a  flame, 
the  antimony  volatilizes,  combines  with  oxygen,  and  deposits 
in  the  cooler  part  of  the  tube  as  amorphous  SbgOg,  antimoni- 
ous oxide,  which  may  sometimes  contain  octahedral  crystals 
of  antimonious  oxide.  (See  Reinsch's  Test  for  Arsenic, 
page  33.) 

7.  Metallic  zinc  reduces  antimonious  solutions,  the  anti- 
mony separating  as  a  black  powder.  If  a  drop  of  the  anti- 
monious solution  is  placed  on  a  piece  of  platinum  foil  and  a 
small  fragment  of  zinc  is  placed  in  the  solution,  the  antimony 
is  deposited  on  the  foil  as  a  brown  or  black  adherent  coating, 
insoluble  in  hydrochloric  acid  : 

2SbCl3  +  Zug  =  Sb2  +  3ZnCl2. 

8.  Compounds  of  antimony,  when  heated  in  the  reducing 
flame  with  sodium  carbonate  on  charcoal,  yield  a  white, 
brittle  globule  of  metallic  antimony,  usually  coated  with  a 
white  incrustation  of  SbgOg,  antimonious  oxide. 

^  As  in  Marsh's  test  for  arsenic.     (See  page  32.) 


40 

BEHAVIOR    OF   ANTIMONY   IN    THE   ANTIMONIC   CONDITION. 

SbClji,  antimonic  chlonde,  may  be  employed  in  mciking  the 


1.  HgS,  hydrogen  sulphide,  precipitates  from  acid  sohi- 
tions  orange-red  SbjSg,  antimonic  sulphide,  insoluble  in  dilute 
acids  and  in  ammonium  carbonate,  soluble  in  concentrated 
hydrochloric  acid,  forming  SbClg,  antimonious  chloride  (with 
the  separation  of  sulphur)  : 

Sh,S,  +  6HC1  =  2SbCl3  -h  3H2S  +  S2, 
and  soluble  in  ammonium  sulphide  and  in  sodium  or  potas- 
sium sulphide,  with  the  formation  or*  sulphantimonates  : 
Sb^Sg  +  S(NH,\S  =  2(NH,)3SbS,. 

2.  The  behavior  of  antimonic  compounds  is  similar  to 
that  of  antimonious  compounds  in  respect  to  the  tests  with 
zinc  and  dilute  sulphuric  acid,  copper  foil  and  hydrochloric 
acid,  and  platinum  foil  and  zinc. 

3.  To  detect  antimonious  compounds  in  the  presence  of 
antimonic  compounds,  advantage  is  taken  of  the  behavior  of 
an  alkaline  solution  of  antimonious  oxide  with  a  silver  solu- 
tion. On  adding  argentic  nitrate  to  the  alkaline  solution 
and  gently  heating  it,  a  precipitate  composed  of  AggO,  argen- 
tic oxide,  and  metallic  silver  is  formed.  Ammonium  hy- 
droxide has  the  property  of  dissolving  only  the  argentic 
oxide,  leaving  the  metallic  silver  undissolved  : 

KaSbOa  +  Ag^O  =-  KSbOg  +  Ag2. 

After  washing  the  precipitate  and  then  treating  it  with 
ammonium  hydroxide,  metallic  silver  will  remain  undis- 
solved in  case  an  antimonious  compound  was  originally 
present. 

To  detect  antimonic  compounds  in  the  presence  of  anti- 
monious compounds,  the  alkaline  solution  is  acidulated  with 


41 

hydrochloric  acid,  KI,  potassium  iodide,  added,  and  then 
boiled ;  in  the  presence  of  an  antimonic;  compound  iodine  is 
separated : 

SbCl^  +  2HI  -=  SbCls  H-  2HC1  -\-  I,. 

TIN,  Sn   (STANNUM). 
Atomic  weight,  119. 0  (118.1) ;  valence,  II,  IV. 

Bluish -white  metal ;  specific  gravity,  7.29  ;  melting-point, 
235°  C. 

Tin  forms  two  series  of  compounds,  named  respectively 
stannous  and  stannic  compounds.  SnO,  stannous  oxide,  may 
be  taken  as  the  type  of  the  stannous,  and  SnOg  as  the  type 
of  the  stannic  compounds. 

BEHAVIOR   OF   TIN    IN    THE   STANNOUS   CONDITION. 

SnCl^f  stannous  chloride^  may  be  employed  in  making  the  tests, 

1.  HgS,  hydrogen  sulphide  (also  ammonium  sulphide), 
precipitates  dark-brown  SnS,  stannous  sulphide,  insoluble  in 
colorless  ammonium  sulphide,  but  easily  soluble  in  yellow 
ammonium  sulphide,  with  the  formation  of  ammonium 
sulphostannate,  (NH4)2SnS3,  a  compound  containing  the  anion 

SnSg'' : 

SnS  +  (NH,)2S2  =  (NH,).SnS3. 

From  this  solution  acids  precipitate  yellow  SnSg,  stannic  sul- 
phide : 

(NH4)2SnS3  +  2HC1  =  SnS^  +  2NH,C1  +  H^S. 

2.  NaOH,  sodium  hydroxide,  as  well  as  KOH,  potassium 
hydroxide,  precipitates  Avhite  Sn(OH)2,  stannous  hydroxide, 
soluble  in  excess  of  the  cold  reagent,  with  the  formation  of  a 
compound  containing  the  anion  Sn02".  On  boiling  a  solu- 
tion of  a  stannous  salt  to  which  an  insufficient  quantity  of 
sodium  or  potassium  hydroxide  has  been  added,  the  Sn(OH)2 
is  converted  into  black  SnO,  stannous  oxide. 

4* 


42 

3.  NH^OH,  ammonium  hydroxide,  precipitates  white 
Sn(OH)2,  stannous  hydroxide,  insoluble  in  excess  of  the 
reagent. 

4.  HgClg,  mercuric  chloride,  added  to  an  excess  of  SnClg, 
stannous  chloride,  j)roduces  a  grayisli  ])recipitate  of  finely- 
divided  metallic  mercury  : 

HgOa  +  SnClg  =  Hg  -f-  SnCl,. 
If,  on  the  other  hand,  an  excess  of  mercuric  chloride  be  added 
to  a  stannous  chloride  solution,  a  white  precipitate  of  HgCl, 
mercurous  chloride,  will  be  formed  : 

2HgCl2  +  SnCl.  =  2HgCl  +  SnCl, 
(a  very  delicate  test  and  a  means  of  distinguishing  between 
stannous  and  stannic  salts). 

5.  A  fragment  of  metallic  zinc  placed  in  a  solution  of 
stannous  chloride  precipitates  grayish  metallic  tin  : 

SnCl2  +  Zn  =  ZnCla  +  Sn. 
If  performed  on  platinum  foil  (see  7  under  Antimony,  page 
39)  the  tin  whicli  separates  does  not  adhere  to  the  platinum 
foil  as  a  black  coating  (distinction  from  antimony). 

6.  Both  stannous  salts  and  stannic  salts,  when  fused  wdth 
sodium  carbonate,  or  with  a  mixture  of  sodium  carbonate  and 
l)otassium  cyanide,  in  the  reducing  flame  on  charcoal,  yield 
white,  ductile  globules  of  metallic  tin  together  with  a  slight 
incrustation  of  SnOg,  stannic  oxide.  Stannic  oxide  moistened 
with  Co(N03)2,  cobaltous  nitrate,  and  heated  in  the  blowpipe- 
flame  becomes  bluish  green  in  color. 

BEHAVIOR   OF   TIN   IN   THE   STANNIC   CONDITION. 

SnCl^j  stannic  chloride^  may  be  employed  in  making  the 
tests. 

1 .  HgS,  hydrogen  sulphide,  precipitates  yellow  SnSg,  stannic 
sulphide,  insoluble  in  ammonium   carbonate,  but  soluble  in 


43 

colorless  and  also  in  yellow  ammonium  sulphide,  with  the 
formation  of  (NH4)2SuS3,  ammonium  sulphostannate,  a  com- 
pound of  the  anion  SnSg''.  From  this  solution  SnS^  is 
reprecipitated  on  the  addition  of  acids.  SnS2  is  soluble  in 
concentrated  hydrochloric  acid. 

2.  NaOH,  sodium  hydroxide,  KOH,  potassium  hydroxide, 
or  NH4OH,  ammonium  hydroxide,  produces  in  sohitions  of 
stannic  salts  white  precipitates.  The  precipitate  produced  in 
hydrochloric  acid  solutions  of  ordinary  SnOg,  stannic  oxide,  is 
Sn(0H)4,  stannic  hydroxide,  and  is  easily  soluble  in  dihite 
sodium  or  potassium  hydroxide,  forming  compounds  contain- 
ing the  anion  Sn03" ;  that  produced  in  solutions  of  meta- 
stannic  acid  is  metastannic  hydroxide,  only  slightly  soluble 
in  excess  of  the  reagent. 

3.  Na2S04,  sodium  sulphate,  or  NH^NOg,  ammonium  ni- 
trate, in  saturated  solution,  added  in  excess  to  a  hydrochloric 
acid  solution  of  stannic  oxide,  precipitates  the  tin,  particularly 
on  the  application  of  heat,  as  white  Sn(OH)4,  stannic  hydrox- 
ide, or  as  (Sn(OH)4)„,  metastannic  hydroxide  : 

SnCl,  +  4Na2SO,  +  4H2O  =  Sn(OH),  +  4NaCl  -f-  4NaHSO, ; 
SnCl^  +  4NH,N03  +  4H20=Sn(OH),  +  4NH,C1  +  4HNO3. 
(Distinction  from  stannous  salts.) 

4.  Metallic  zinc  reduces  stannic  salts  in  solution  to  metallic 
tin  in  the  same  manner  as  it  reduces  stannous  salts.  (See  5, 
page  42). 

CADMIUM,  Cd. 
Atomic  weight,  112.4-  (111.6) ;  valence,  11. 

Bluish-white  metal ;  specific  gravity,  8.54 ;  melting-point, 
315°  C. 

CdSO^y  cadmium  sulphate^  may  be  employed  in  making  the 
tests. 

1.  H2S,  hydrogen  sulphide,  or  ammonium  sulphide,  pro- 


44 

duces  a  yellow  precipitate  of  CdS,  cadmium  sulphide,  in- 
soluble in  dilute  acids,  in  ammonium  and  sodium  sulphides, 
and  in  potassium  cyanide,  soluble  in  boiling  nitric  acid,  with 
the  formation  of  Cd(N03)2,  cadmium  nitrate. 

2.  NaOH,  sodium  hydroxide,  as  well  as  KOH,  potassium 
hydroxide,  precipitates  white  Cd(OH)2,  cadmium  hydroxide, 
insoluble  in  excess  of  the  reagent. 

3.  NH4OH,  ammonium  hydroxide,  precipitates  white 
Cd(OH)2,  cadmium  hydroxide,  soluble  in  excess  of  the  re- 
agent, probably  with  the  formation  of  a  colorless  double  salt 
of  cadmium  and  ammonium,  Cd(NH3)4S04,  containing  the 
complex  cation  Cd(NH3)4' '. 

4.  KCN,  potassium  cyanide,  added  to  a  neutral  or  ammo- 
niacal  solution  of  a  cadmium  salt,  precipitates  wliite  Cd(CN)2, 
cadmium  cyanide,  which  is  soluble  in  an  excess  of  potassium 
cyanide,  forming  a  colorless  solution  of  K2Cd(CN)^ : 

CdSO,  -f-  2KCN  =  Cd(CN)2  +  K^SO^ ; 

Cd(CN)2  +  2KCN  -=  K2Cd(CN),. 
Hydrogen   sulphide  precipitates    from   this    solution  yellow 
CdS,  cadmium  sulphide. 

(This  cyanide  is  the  potassium  compound  of  the  anion 
Cd(CN)/' ;  cadmium  ions  are  dissociated  from  it,  so  that,  in 
contrast  with  copper,  the  cadmium  is  precipitated.) 

5.  Cadmium  compounds  mixed  with  sodium  carbonate 
and  fused  in  the  reducing  flame  on  charcoal,  yield  yellow  to 
brown  incrustations  of  CdO,  cadmium  oxide. 

GOLD,  Au  (AURUM). 
Atomic  weight,  197.2  (195.7)  ;  valence,  I,  MF. 
Yellow    metal;    specific    gravity,    19.26;    melting-point, 
1035°  C. 

AuCl^^  amnc  Ghloride,  may  he  employed  in  mahing  the  fesfa. 
1.  HgS,  hydrogen  sulphide,  produces  in  a  cold  solution  of 


45 

auric  chloride  a  black  precipitate  of  AugSg,  auric  sulphide, 
soluble  in  ammonium  sulphide. 

From  hot  auric  chloride  solutions  hydrogen  sulphide  pre- 
cipitates brownish  metallic  gold  : 

8 AUCI3  -f  3H2S  +  1 2H2O  =  Aug  +  24HC1  -f  3H2SO4. 
2.  NaOH,  sodium  hydroxide,  and  also  potassium  hydrox- 
ide  precipitate    reddish-yellow,  amorphous   Au(OH)3,  auric 
hydroxide,  soluble  in  excess  of  the  reagent. 

3.  NH4OH,  ammonium  hydroxide,  produces  a  reddish- 
yellow  precipitate  of  (NH3)2Au203,  ammonium  aurate  (fulmi- 
nating gold)  : 

2AUCI3  +  8NH,OH  =  (NH3)2Au  A  +  6NH,C1  +  SH^O. 

4.  FeSO^,  ferrous  sulphate,  precipitates  in  the  presence  of 
a  free  mineral  acid,  even  in  the  cold,  but  especially  on  heating, 
metallic  gold,  brownish  in  color  because  of  its  finely-divided 
condition  : 

2AUCI3  +  eFeSO^  =  Au2  +2FeCl3+  2Fe2(S04)3. 

5.  H2C2^4,  oxalic  acid,  also  precipitates  metallic  gold  from 
auric  chloride  solutions : 

2AUCI3  +  3H2C2O,  -=  Au2  +  6HC1  +  6CO2. 
The  precipitation  proceeds  slowly,  but  is  complete.     WaVm- 
ing  the  solution  facilitates  the  reduction.     The  presence  of 
considerable  free  mineral  acid  interferes  with  the  precipitation. 

6.  SnClg,  stannous  chloride,  especially  in  very  dilute  solu- 
tion, added  to  auric  chloride  solutions,  produces  a  purplish- 
red  coloration  or  a  purplish-red  precipitate  (purple  of  Cassius), 
consisting  probably  of  a  mixture  of  finely-divided  gold  and 
stannic  oxide. 

7.  Compounds  of  gold  fused  with  sodium  carbonate  or 
with  bomx  on  charcoal  yield  yellow,  glistening,  ductile 
spangles  of  metallic  gold. 


46 

PLATINUM,   Pt. 
Atomic  weight,  194-.8  (193.3)  ;  valence,  II,  IV. 
Tin-white  metal;   specific  gravity,  21.46;   melting-point, 
1775°  C. 

H2PtClQy  hydrochlorplaiiniG  acid  (or  PtCl^,  platmic  chlo- 
ride), may  be  employed  in  makiyig  the  tests, 

1.  HgS,  hydrogen  sulphide,  produces  in  cold  platinic  chlo- 
ride solutions  a  brownish  coloration,  but  after  some  time  has 
elapsed  a  brownish-black  precipitate  of  PtSg,  platinic  sulphide, 
separates.  The  precipitate  appears  at  once  on  heating  the 
solution.  The  precipitate  is  insoluble  in  hydrochloric  acid 
and  also  in  nitric  acid,  but  soluble  in  nitro-hydrochloric  acid 
(aqua  regia)  and  also  in  ammonium  sulphide. 

2.  KNO3,  potassium  nitrate,  to  which  a  drop  of  hydro- 
chloric acid  has  been  added,  or  potassium  chloride,  added  to 
a  concentrated  solution  of  platinic  chloride,  produces  a  yellow 
crystalline  precipitate  of  KgPtCIg,  potassium  chlorplatinate, 
slightly  soluble  in  water,  insoluble  in  alcohol.  The  test  is 
best  made  in  a  watch-glass,  the  liquid  being  stirred  with  a 
glass  rod.     Addition  of  alcohol  facilitates  precipitation. 

3.  NH4CI,  ammonium  chloride,  produces  a  yellow  crystal- 
line precipitate  of  (NH4)2PtClg,  ammonium  chlorplatinate, 
slightly  soluble  in  water,  insoluble  in  alcohol.  This  test  is 
best  made  in  a  watch-glass  as  in  2,  above. 

4.  Compounds  of  platinum  heated  in  the  reducing  flame 
are  reduced  to  spongy  metallic  platinum. 


THIRD   GROUP. 


Metals  precipitated  as  hydroxides  by  NH/)H,  ammonium 
liydroxide :   Iron,  Aluminium,  and  Chromium   (cations  Fe' ', 

rV",  Ar*-,  Cr'--). 


47 

The  members  of  this  group,  with  the  exception  of  iron,  are 
also  precipitated  as  hydroxides  by  (SH^^S,  ammonium  sul- 
phide, but  are  not  precipitated  from  neutral  or  acid  solutions 
by  hydrogen  sulphide : 

AICI3  +  3NHPH  =  Al(OH)3  -h  3NH,C1. 
2CrCl3+  3(NH,)2S  +  BHp  =  2Cr(OH)3-j-  SH^S  +  6NH,C1. 

Chromic  hydroxide  is  perceptibly  soluble  in  cold  anmio- 
nium  hydroxide  (imparting  a  reddish  tint  to  the  liquid),  form- 
ing complex  chromium  ammonia  hydroxides — combinations  of 
the  cation  Cr(NH3)g*  *  * — which  may  be  decomposed  by  boiling. 

Recently   precipitated    moist    BaCOg,   barium   carbonate, 
also  precipitates,  even  from  cold  solutions,  the  members  of 
this  group  as  hydroxides  (together  with  basic  salts)  : 
2AICI3  +  3BaC03  +  3H2O  -  2Al(OH)3  +  BaCl^  +  3CO2. 

The  presence  of  tartaric  acid,  citric  acid,  and  other  organic 
substances  prevents  or  at  least  retards  the  precipitation  of 
the  members  of  this  group  as  hydroxides  by  the  formation 
of  complex  compounds. 

IRON,   Fe  (FERRUM). 
Atomic  weight,  55.9  (55.5) ;  valence,  H,  III. 

Silver-white  metal ;  specific  gravity,  7.84. 

Iron  forms  two  typical  series  of  compounds,  named  re- 
spectively ferrous  and  ferric  compounds.  FeO,  ferrous  oxide, 
may  be  taken  as  the  type  of  the  ferrous  compounds,  and 
FcgOg  as  the  type  of  the  ferric  compounds. 

BEHAVIOR   OF   IRON   IN   THE   FERROUS   CONDITION. 

FeSO^j  ferrous  sulphate,  may  be  employed  in  making  the 


1.  NH^OH,   NaOH,  or  KOH  precipitates,  in  solutions 
of  ferrous   salts  which  are  free  from  dissolved  air,   white 


48 

Fe(OH)2,  ferrous  hydroxide,  which,  by  the  absorption  of 
oxygen,  quickly  changes  in  color  to  green,  black,  and  finally 
to  reddish  brown.  The  presence  of  ammonium  chloride  or 
sulphate  retards  the  precipitation,  therefore  it  is  incom- 
plete— due  to  the  formation  of  (NH^)2FeCl4,  as  in  the  case 
of  magnesium ;  nevertheless,  from  these  alkaline  solutions, 
in  consequence  of  the  absorption  of  oxygen,  black  ferrous 
hydroxide  and  reddish-brown  ferric  hydroxide  gradually 
separate. 

2.  (NHJgS  precipitates  black  FeS,  ferrous  sulphide,  insol- 
uble in  excess  of  the  reagent,  easily  soluble  in  hydrochloric 
acid  and  in  nitric  acid.  Very  dilute  ferrous  solutions  are 
colored  green  by  ammonium  sulphide.  Moist  ferrous  sul- 
phide is  oxidized  on  exposure  to  the  air  and  changes  to 
reddish-brown  Fe20(S04)2,  basic  ferric  sulphate. 

3.  K4Fe(CN)g,  potassium  ferrocyanide,  produces  in  ferrous 
solutions  free  from  ferric  salts  a  white  precipitate,  which 
quickly  changes  to  bluish-white  K2Fe(Fe(CN)6),  potassium 
ferrous  ferrocyanide  (Everett's  salt),  insoluble  in  acids.  On 
exposure  to  air  the  bluish-white  precipitate  gradually  absorbs 
oxygen  and  changes  to  blue  Fe^(Fe(CN)6)3,  ferric  ferrocyanide 
(Prussian  blue) : 

4K2Fe(Fe(CN)e)  +  O2  -f  4HC1  =  Fe,(Fe(CN)e)3  + 
K,Fe(CN)e  +  4KC1  +  2H2O. 

4.  K3Fe(CN)g,  potassium  ferricyanide,  precipitates  dark- 
blue  Fe3(Fe(CN)6)2,  ferrous  ferricyanide  (Turnbull's  blue), 
insoluble  in  acids. 

5.  KCNS,  potassium  sulphocyanide,  does  not  produce  a 
claret-red  coloration  in  solutions  of  ferrous  salts  free  from 
ferric  salts.     (Distinction  from  ferric  salts.) 

6.  Ferrous  salts  when  warmed  with  nitric  acid  are  oxi- 
dized to  ferric  salts,  in  which  Fe'  *  is  converted  into  Fe'  *  ', 
BFeSO^  -h  2HNO3  +  3H2SO,  --  3Fe2(SO J3  +  2NO  +  4H2O. 


49 

7.  Ferrous  compounds  and  also  ferric  compounds  when 
ignited  with  sodium  carbonate  on  charcoal  yield  a  black 
magnetic  oxide. 

8.  All  compounds  of  iron  when  fused  in  the  oxidizing 
flame  in  a  bead  of  borax  yield  while  hot  a  yellow  or  reddish- 
brown  bead,  which  on  cooling  becomes  lighter  in  color  or 
colorless.  Fused  in  the  reducing  flame  the  bead  becomes 
bottle-green  in  color. 

BEHAVIOR   OF    IRON   IN   THE    FERRIC   CONDITION. 

FeCl^jfei^ric  chloride,  may  be  employed  in  making  the  tests. 

1.  NH4OH,  NaOH,  or  KOH,  produces  in  solutions  of 
ferric  salts  a  voluminous  reddish-brown  precipitate  of 
Fe(OH)3,  ferric  hydroxide,  insoluble  in  excess  of  the  reagent 
and  in  ammonium  salts. 

2.  (XH4)2S  precipitates  black  FeS  together  with  free  sul- 
phur : 

2FeCl3  +  3(NH4)2S  =  2FeS  +  S  +  6NH,C1. 

3.  K4Fe(CN)g,  potassium  ferrocyanide,  precipitates,  even 
in  exceedingly  dilute  solutions  of  ferric  salts,  blue 
Fe4(Fe(CN)g)3,  ferric  ferrocyanide  (Prussian  blue),  insoluble 
in  acids,  but  decomposed  by  alkalies. 

4.  K3Fe(CN)g,  potassium  ferricyanide,  does  not  produce  a 
precipitate  in  ferric  solutions,  but  imparts  a  green  or  brown 
coloration  to  the  solution.     (See  3,  page  96.) 

5.  KCNS,  potassium  sulphocyanide,  produces  an  intense 
claret-red  colomtion  in  ferric  solutions,  due  to  the  formation 
of  soluble  Fe(CNS)3,  ferric  sulphocyanide.  In  exceedingly 
dilute  solutions  the  color  is  pale  red.  On  agitating  the  solu- 
tion with  ether  the  ferric  sulphocyanide  will  be  extracted 
from  the  aqueous  solution  because  the  sulphocyanide  is  not 
dissociated.  HgClg,  mercuric  chloride,  destroys  the  colora- 
tion, soluble  Hg(CNS)2  being  formed. 


50 

6.  NaC2H302,  sodium  acetate,  added  to  a  solution  of  a 
ferric  salt  which  contains  little  free  mineral  acid,  colors  the 
solution  dark  red,  due  to  the  formation  of  Fe(C2H302)3,  ferric 
acetate,  which  on  boiling  the  sufficiently  diluted  solution 
hydrolyzes  and  separates  with  part  of  the  acetic  acid  as  a 
brownish-red  flocculent  precipitate  of  Fe(OH)2(C2H302), 
basic  ferric  acetate : 

Fe(C2H302)3  -h  2H2O  =  Fe(OH)2C2H302  +  2HC2H3O2. 

7.  Barium  carbonate  when  added  in  moist  condition  pro- 
duces a  precipitate  of  Fe(OH)3,  ferric  hydroxide. 

8.  H2S,  hydrogen  sulphide,  reduces  ferric  salts  in  solution 
to  ferrous  salts,  with  the  separation  of  sulphur  : 

2FeCl3  +  H2S  =  2FeCl2  +  2HC1  +  S. 

9.  Metallic  zinc  and  hydrochloric  acid  reduce  ferric  salts 
to  ferrous  salts  ;  sulphurous  acid  also  acts  as  a  reducing  agent 
(conversion  of  Fe*  *  *  to  Fe' ')  : 

2FeCl3  +  Zn  =  2FeCl2  +  ZnCla- 
2FeCl3  +  H2SO3  +  H2O  =  2FeCl2  +  H2SO,  +  2HC1. 

10.  For  the  behavior  of  ferric  salts  on  charcoal  and  in  the 
borax  bead  see  under  Ferrous  Salts,  7  and  8,  page  49. 

ALUMINIUM,   AI. 
Atomic  weight,  27.1  (26.9)  ;  valence,  III. 
Tin-white  metal;  specific  gravity,    2.56  (specific   gravity 
of  the  hammered  metal,  2.67) ;  melting-point,  about  700°  C. 
Alj^SO^^j  aluminium  sulphate,  or  NH^Al{80^)2,  ammonium 
alumiriium   sulphate  (ammonia   alum),   may  he   employed   in 
making  the  tests. 

1.  NH4OH  precipitates  white  gelatinous  Al(OH)3,  alumin- 
ium hydroxide,  slightly  soluble  in  an  excess  of  the  reagent. 
The  precipitation  is  complete  only  when  the  excess  of  am- 
monia has  been  driven  off  by  boiling  the  solution. 

2.  NaOH    or    KOH     precipitates    gelatinous    A1(0H)3, 


51 

aluminium  hydroxide,  soluble  in  an  excess  of  either  reagent, 
with  the  formation  of  NagAlOg,  sodium  aluminate,  or 
K3AIO3,  potassium  aluminate,  due  to  the  combination  of  the 
sodium  or  potassium  with  the  trivalent  anion  AIO3"' : 

Al(OH)3  +  3NaOH  =  Na3A103  +  SUfi. 
As  aluminium  hydroxide  is  insoluble  in  ammonium  hydrox- 
ide (providing  the  latter  is  not  present  in  great  excess),  the 
aluminium  hydroxide  may  be  reprecipitated  from  its  solution 
as  aluminate  by  the  addition  of  ammonium  chloride : 

Na3A103  4-  3NH,C1  =  Al(OH)3  +  3NH3  +  3NaCl. 
Aluminium  hydroxide  is  somewhat  soluble  in  water,  but  not 
in  water  containing  ammonium  salts  ;  when  in  aqueous  solu- 
tion it  is  believed  to  be  in  the  colloidal  state. 

Boiling  does  not  decompose  the  aluminates.  The  solutions 
of  aluminates  have  an  alkaline  reaction. 

3.  (NHjgS  completely  precipitates  aluminium  from  its 
solution  as  Al(OH)3,  aluminium  hydroxide,  with  the  evolu- 
tion of  hydrogen  sulphide. 

4.  Na2HP04,  sodium  hydrogen  phosphate,  precipitates  in 
neutral  solutions  white  gelatinous  AlPO^,  aluminium  phos- 
phate, insoluble  in  acetic  acid  and  in  ammonium  hydroxide, 
soluble  in  mineral  acids  and  in  sodium  or  potassium  hydrox- 
ide, with  the  formation  of  aluminates  : 

AlPO,  +  6NaOH  =  Na3A103  +  Na3PO,H-  3H.O. 
Ammonium  chloride  reprecipitates  the  aluminium  phosphate 
from  its  solution  in  sodium  or  potassium  hydroxide : 
Na3A103  H-  Na3PO,  +  6NH,C1  =  AlPO,  -f  6NaCl  +  6NH3 

-h  3H2O. 

5.  Na2S203,  sodium  hyposulphite,  added  to  a  neutral  solu- 
tion of  a  salt  of  aluminium  precipitates  white  gelatinous 
Al(OH)3,  with  the  separation  of  free  sulphur  and  liberation 
of  SO2,  sulphurous  anhydride.  Complete  precipitation  takes 
place  only  when  the  solution  of  the  aluminium  salt  is  dilute 


52 

and  is  boiled,  after  the  addition  of  the  hyposulphite,  until  the 
odor  of  sulphurous  anhydride  can  no  longer  be  detected  : 
2AICI3  +  SNa^SA  H-  3H2O  -  2Al(OH)3  +  6NaCl  +  SSO^ 

+  S3. 

6.  NaC2H302,  sodium  acetate,  added  in  excess  to  a  solution 
of  an  aluminium  salt,  and  the  solution  diluted  with  water 
and  boiled,  produces  a  precipitate  of  Al(OH)2C2H302,  basic 
aluminium  acetate.  Neutral  aluminium  acetate  is  first  pro- 
duced when  the  sodium  acetate  is  added,  and  this  on  boiling 
the  liquid  is  converted  by  hydrolysis  into  insoluble  basic 
aluminium  acetate  and  acetic  acid  : 

Al2(SO,)3  +  6NaC2H302  =  2A1(C2H302)3  +  3Na2SO, ; 
A1(C2H302)3  +  2H2O  =  Al(OH)2C2H302  +  2HC2H3O2. 

7.  BaCOa,  barium  carbonate,  when  added  in  moist  con- 
dition precipitates  Al(OH)3,  aluminium  hydroxide. 

8.  Compounds  of  aluminium  mixed  with  sodium  carbon- 
ate and  ignited  on  charcoal  yield  white  infusible  aluminium 
oxide ;  on  moistening  the  mass  with  cobaltous  nitrate  and 
again  igniting,  an  infusible  blue  residue  is  obtained,  due  to 
the  combination  of  CoO,  cobaltous  oxide,  with  AI2O3,  alumin- 
ium oxide  (Thenard^s  blue). 

CHROMIUM,  Cr. 
Atomic  weight,  52.1  (51.7) ;  valence,  11,  ril. 
Light-gray  crystalline  powder;  specific  gravity,  6.81. 
CrC/3,  chromic  chloride,  may  he  employed  in  making  the  tests. 

1.  NH4OH  precipitates  bluish-green  or  grayish-green  ge- 
latinous Cr(OH)3,  chromic  hydroxide ;  if  the  precipitation 
has  taken  place  in  a  cold  solution,  a  small  quantity  of  chromic 
oxide  will  remain  dissolved  in  the  ammonium  hydroxide ;  on 
boiling  this  purplish  solution  all  of  the  chromium  is  precipi- 
tated as  chromic  hydroxide. 

2.  NaOH  or  KOH  precipitates  from  solutions  of  both  the 


53 

green  and  the  violet  salts  of  chromium  greenish  flocculent 
Cr(OH)3,  chromic  hydroxide,  soluble  in  an  excess  of  the 
reagent,  forming  NagCrOg,  sodium  chromite,  in  consequence 
of  the  production  of  the  anion  CrOg'^',  and  imparting  a 
greenish  color  to  the  solution  : 

Cr(OH)3  -F  3NaOH  =  NagCrOa  +  SUfi. 
From  this  solution  chromic  hydroxide  is  reprecipitated  by  the 
addition  of  ammonium  chloride  or  by  long-continued  boiling : 

NagCrOs  +  SHp  =  Cr(OH)3  +  3NaOH. 
The  reaction  with  NaOH  is  reversible  : 

Cr(OH)3  +  SNaOH^^^NagCrOg  +  3H2O. 

Th§  precipitated  chromic  hydroxide  obtained  by  boiling  its 
alkaline  solution  appears  to  be  insoluble  in  sodium  or  potas- 
sium hydroxide.  It  is  probably  a  chromic  hydroxide  some- 
what deficient  in  water  of  hydration.  The  solubility  of 
chromic  hydroxide  in  sodium  hydroxide  is  very  much  re- 
tarded by  the  presence  of  ferric  hydroxide. 

3.  NaC2H302,  sodium  acetate,  will  not  precipitate  chro- 
mium as  a  basic  acetate,  as  in  the  case  of  aluminium. 

4.  (NH4)2S  precipitates  Cr(OH)3,  chromic  hydroxide,  with 
the  evolution  of  liydrogen  sulphide  : 

2CrCl3  +  3(NH,)2S  +  GH^O  =  2Cr(OH)3  +  6NH4CI  +  3H2S. 

5.  Bromine  water,  or  chlorine  water,  added  to  a  chromium 
solution,  which  has  previously  been  rendered  alkaline  with 
NaOH  or  KOH,  and  warmed,  changes  the  green  color  of 
the  solution  to  yellow,  due  to  the  formation  of  a  chromate 
of  the  alkali  : 

K3Cr03  +  3Br  +  2KOH  =  K^CrO,  +  3KBr  +  H^O. 
On  neutralizing  the    solution  with  acetic  acid  and  adding 
plumbic  acetate,  a  yellow  precipitate  of  PbCrO^,  plumbic 
chromate,  will  be  produced  : 

K^CrO.-f  Ph{C,lIf>,%=  PbCrO,  +  2KC2H3O2. 

5* 


54 

In  this  case  the  anion  CrOg"'  is  transformed  into  the  chromate 
anion  CrO^''.  Also  on  boiling  an  alkaline  (NaOH  or  KOH) 
solution  of  chromium  with  lead  peroxide  a  yellowish  coloration 
is  imparted  to  the  liquid,  due  to  the  formation  of  a  chromate  : 

2K3Cr03  -h  3Pb02  =  2K2CrO,  +  2PbO  +  K^PbO^. 

The  lead  oxide  (PbO)  remains  in  solution  in  the  excess  of 

alkali.     On  acidulating  with  acetic  acid  the  lead  separates 

as  yellow  PbCrO^,  plumbic  chromate  : 

K^PbO^  +  K^CrO,  -f  4HC,H30,  =  PbCrO,  +  4KC,JI,0, 

-f  2H,0. 

6.  A  salt  of  chromium,  fused  on  platinum  foil  with  a 
mixture  of  sodium  carbonate  and  potassium  nitrate  or  potas- 
sium chlorate,  yields  a  mass  containing  a  salt  of  chromic 
acid — i.  e.y  a  chromate ;  on  exhausting  the  mass  with  water  a 
yellow  solution  of  Na2Cr04,  sodium  chromate,  and  K2Cr04, 
potassium  chromate,  is  obtained  which,  when  acidulated  with 
acetic  acid  and  treated  with  plumbic  acetate,  yields  a  yellow 
precipitate  of  PbCrO.^,  plumbic  chromate  : 

CrA  +  2Na2C03  +03=  2Na2Cr04  +  2CO2 ; 
Na2Cr04  -f  Pb(C2H302)2  =  PbCrO^  +  2NaC2H302. 

7.  Compounds  of  chromium  when  ignited  with  sodium  car- 
bonate on  charcoal  yield  a  green  fused  mass  containing  oxides 
of  chromium. 

8.  Fused  in  a  bead  of  borax  or  of  microcosmic  salt,  in 
either  the  oxidizing  or  the  reducing  flame,  chromium  com- 
pounds yield  a  yellowish-green  bead,  which  becomes  emerald- 
green  on  cooling. 

FOURTH   GROUP. 

Metals  precipitated  as  sulphides  from  neutral  solutions  by 
(NH4)2S,  ammonium  sulphide :  Manganese,  Zinc,  Cobalt,  and 
Nickel  (cations  Mn  ",  Zn* ',  Co'  *,  Ni '  *).  In  addition  to  their 
being  precipitated  by  ammonium  sulphide  as  sulphides,  they 


55 

are  precipitated  by  ammonium  hydroxide  and  sodium  or  po- 
tassium hydroxide  as  hydroxides.  Certain  of  these  hydrox- 
ides are  soluble  in  an  excess  of  the  reagent — ammonium  hy- 
droxide dissolves  the  hydroxides  of  cobalt,  nickel,  and  zinc ; 
sodium  or  potassium  hydroxide  dissolves  zinc  hydroxide. 
Excepting  ferric  salts,  they  are,  in  general,  not  precipitated  in 
the  presence  of  ammonium  salts.  Hydrogen  sulphide  will 
not  cause  precipitation  in  their  solutions  if  they  contain  free 
mineral  acids. 

MANGANESE,  Mn. 
Atomic  weight,  55. 0  (54.6);  valence,  II,  III. 
Grayish-white  metal ;  specific  gravity,  about  8. 

MnSO^,  manganous  sulphate^  may  be  employed  in  making 
the  tests. 

1.  (NH4)2S  precipitates  pale-salmon-colored  MnS,  manga- 
nous sulphide,  containing  water,  easily  soluble  in  acetic  acid 
and  in  hydrochloric  acid.  (Occasionally,  especially  after 
standing  some  time,  the  pale-salmon-colored  precipitate  con- 
taining water  is  converted  into  green  MnS,  manganous  sul- 
phide, which  is  free  from  water.)  Manganous  sulphide 
readily  oxidizes  on  exposure  to  the  air  and  becomes  dark 
brown,  due  to  the  formation  of  HgMnO,,  hydrated  peroxide 
of  manganese. 

2.  NaOH  or  KOH  precipitates  white  Mn(OH)2,  manganous 
hydroxide,  insoluble  in  excess  of  the  reagent.  On  exposure 
to  the  air  the  precipitate  rapidly  becomes  brown,  due  to  the 
formation  of  Mn(OH)3,  manganic  hydroxide.  Manganous 
hydroxide  is  soluble  in  ammonium  chloride,  owing  to  the 
production  of  a  double  salt,  whereas  manganic  hydroxide  is 
insoluble  in  that  reagent ;  on  this  account  anniionium  chloride 
solutions  of  manganous  hydroxide  containing  free  ammonia 


56 

become  brown  on  exposure  to  the  air,  due  to  the  separation 

of  manganic  liydroxide : 

Mn(OH)2  +  4NH,C1  =  (NHJ^MnCl,  +  2H2O  +  2NH3 ; 

2(NH,)2MnCl,  +  4NH3  +  5H2O  +  O  ^  2Mn(OH)3  + 

8NH,C1. 

3.  NH4OH  precipitates  in  neutral  solutions,  and  also  in 
solutions  free  from  salts  of  ammonium,  white  Mn(OH)2, 
manganous  hydroxide ;  in  the  presence  of  salts  of  ammonium 
or  of  free  acids,  excess  of  ammonium  hydroxide  fails  to  pro- 
duce a  precipitate,  because  of  the  formation  of  a  soluble 
double  salt  of  manganous  hydroxide  with  the  ammonium 
salts.  The  action  of  the  oxygen  of  the  air  converts  the  solu- 
ble manganous  salt  into  Mn(OH)3,  manganic  hydroxide, 
which  separates  as  a  brown  precipitate. 

4.  Na2C03,  sodium  carbonate,  or  K2CO3,  potassium  carbo- 
nate, precipitates  white  MnCOg,  manganous  carbonate,  but 
previously  moistened  barium  carbonate  does  not  produce  a 
precipitate. 

5.  NaC2H302,  sodium  acetate,  does  not  produce  a  precipi- 
tate in  boiling  solutions  of  salts  of  manganese.  (Distinction 
from  ferric  salts.) 

6.  Bromine  water  added  to  an  alkaline  solution  of  a  man- 
ganese salt  produces  a  precipitate  of  brown  hydrated  peroxide 
of  manganese : 

MnCl2  +  2NaOH  +  NaBrO  =  H2Mn03  +  2NaCl  +  NaBr. 

7.  Concentrated  nitric  acid  and  an  excess  of  Pb02,  lead 
peroxide,  added  to  a  solution  of  a  manganese  salt  produce,  on 
warming  the  liquid,  a  red  solution,  due  to  the  formation  of 
permanganic  acid  : 

2MnS04  +  6HNO3  -h  5Pb02  --  2HMnO,  +  2PbS0,  + 
3Pb(N03)2  -f  2H2O. 
The  red  coloration  is  especially  observable  on  permitting  the 
excess  of  Pb02  to  subside. 


57 

8.  Compounds  of  manganese,  fused  on  platinum  foil  with 
sodium  carbonate  and  potassium  nitrate,  yield  a  bluish-green 
mass  containing  manganates  of  sodium  and  potassium,  com- 
pounds of  the  divalent  manganate  ion  MnO^'': 
3Mn(OH)2  +  Na2C03  +  4KNO3  =  Na^MnO,  +  2K2MnO,  + 

4NO  +  CO2  +  3H2O. 
The  test  is  an  exceedingly  delicate  one,  and  only  a  minute 
quantity  of  a  salt  of  manganese  need  be  used. 

On  exhausting  the  mass  with  water,  soluble  KMnO^, 
potassium  permanganate  (a  compound  of  the  univalent  per- 
manganate ion  MnO/),  and  insoluble  brown  HgMnOg,  hy- 
drated  peroxide  of  manganese,  are  formed  : 

3K2Mn04  +  3H2O  =  2KMnO,  +  H^MnOg  +  4KOH. 
The  potassium  permanganate  dissolves,  imparting  a  purplish- 
red  color  to  the  water. 

9.  Compounds  of  manganese,  fused  in  the  oxidizing  flame 
in  a  bead  of  borax  or  of  microcosmic  salt,  yield  an  amethyst- 
colored  bead ;  fused  in  the  reducing  flame,  the  bead  becomes 
colorless. 

ZINC,  Zn. 
Atomic  weight,  65.4  (64.9) ;  valence,  IF. 

Bluish-white  metal ;  specific  gravity,  6.9 ;  melting-point, 
433°  C. 

ZnSO^,  zinc  sulphate,  may  be  employed  in  making  the  tests. 

1.  (NH4)2S  precipitates  white  ZnS,  zinc  sulphide,  easily 
soluble  in  hydrochloric  acid,  insoluble  in  acetic  acid. 

2.  NaOH  or  KOH  precipitates  white,  gelatinous  Zn(OH)2, 
zinc  hydroxide,  soluble  in  excess  of  the  reagent,  with  the 
formation  of  NaaZnOg,  sodium  zincate,  or  KgZnOg,  potassium 
zincate,  compounds  of  the  zinc  anion  ZnOg'': 

Zn(OH)2  -h  2NaOH  =  Na2Zn02  +  2H2O. 


58 

These  solutions,  which  have  an  alkaline  reaction,  yield  a  precipi- 
tate of  ZnS,  zinc  sulphide,  on  the  addition  of  hydrogen  sulphide. 

3.  NH4OH  precipitates  in  neutral  solutions  white  floccu- 
lent  Zn(OH)2,  zinc  hydroxide,  soluble  in  excess  of  the  reagent, 
with  the  formation  of  complex  zinc  ammonia  compounds : 

Zn(0H)2  +  2NHPH  =  {^RX^nO^i  +  2Hp. 

4.  K4Fe(CN)g,  potassium  ferrocyanide,  produces  a  white 
flocculent  precipitate  of  Zn2Fe(CN)g,  zinc  ferrocyanide,  insol- 
uble in  acids  and  in  ammonium  hydroxide.  The  precipitate 
while  in  suspension  often  has  a  pale-yellowish  appearance, 
due  to  the  color  imparted  to  the  liquid  by  the  presence  of  an 
excess  of  potassium  ferrocyanide. 

5.  NaaCO,,  sodium  carbonate,  or  K2CO3,  potassium  car- 
bonate, precipitates  white  basic  zinc  carbonate.  Ammonium 
carbonate  likewise  produces  a  precipitate  of  white  basic  zinc 
carbonate,  which  is  soluble  in  cold  solutions  in  an  excess  of 
the  reagent.  Recently  precipitated  moist  BaCOg,  barium 
carbonate,  fails  to  produce  a  precipitate. 

6.  NaC2H302,  sodium  acetate,  does  not  produce  a  precipi- 
tate in  boiling  solutions  of  zinc  salts. 

7.  Compounds  of  zinc,  ignited  with  sodium  carbonate  in 
the  reducing  flame  on  charcoal,  yield  a  coating  of  ZnO,  zinc 
oxide,  which  is  yellow  when  hot  and  white  when  cold.  On 
moistening  the  deposit  with  cobaltous  nitrate  and  again  ignit- 
ing, the  deposit  becomes  green  in  color. 

COBALT,  Co. 
Atomic  weight,  59. 0  (58.56)  ;  valence,  II,  III. 

Steel-gray  metal ;  specific  gravity,  8.6. 

Co{N0^2y  cobaltous  nitrate^  or  CoCl^y  cobaltous  chloride, 
may  be  employed  in  making  the  tests. 

1.  (NH4)2S  precipitates  black  CoS,  cobaltous  sulphide,  in- 


59 

soluble  in  excess  of  colorless  ammouium  sulphide  and  in  dilute 
hydrochloric  acid;  soluble  in  nitro-hydrochloric  acid,  with 
the  formation  of  CoClg,  cobaltous  chloride : 
3CoS  +  6HC1  -[-  2HNO3  =  3C0CI2  +  S3  +  2NO  +  4H2O. 

2.  NaOH  or  KOH  precipitates  in  cold  cobaltous  solu- 
tions a  bluish  basic  salt,  and  in  boiling  solutions  rose-red 
Co(OH)2,  cobaltous  hydroxide.  Both  precipitates  become 
oxidized  on  exposure  to  the  air  and  turn  olive-green  in  color. 
They  are  insoluble  in  excess  of  the  reagent. 

3.  NH4OH  precipitates  in  cold  cobaltous  solutions  a  bluish 
basic  salt,  and  in  boiling  solutions  rose-red  Co(OH)2,  cobaltous 
hydroxide.  Both  of  these  precipitates  are  soluble  in  an  excess 
of  the  concentrated  reagent,  imparting  a  reddish  color  to  the 
liquid,  which,  on  exposure  to  the  oxidizing  action  of  the  air, 
soon  changes  to  brown,  owing  to  the  production  of  cobalt  am- 
monia ions.  The  presence  of  ammonium  salts  prevents  the 
precipitation. 

4.  KCN,  potassium  cyanide,  precipitates  brownish- white 
Co(CN)2,  cobaltous  cyanide,  soluble  in  excess  of  the  reagent, 
with  the  formation  of  K4Co(CN)g,  potassium  cobaltous  cyan- 
ide. On  boiling  this  solution  in  tlie  presence  of  an  excess 
of  potassium  cyanide,  or  in  the  presence  of  an  excess  of 
potassium  hydroxide  (or  of  sodium  hydroxide),  or  on  adding 
bromine  water,  a  precipitate  of  potassium  cobaltic  cyanide, 
K3Co(CN),;,  the  potassium  compound  of  the  com|)lex  anion 
Co(CNy,  is  produced — /.  r.,  the  cobaltous  cyanogen  ion 
Co(CN),/'''  is  transformed  into  the  cobaltic  cyanogen  ion 
Co(CN)/''.  Acids  added  to  this  solution  do  not  precipitate 
cobaltous  cyanide : 

C0CI2  +  2KCN  =  Co(CN)2  -f  2KC1 ; 
Co(CN)2  +  4KCN  -  K,Co(CN)«. 

2K,Co(CN),  +  O  +  HP  -=  2K3Co(CN),  f  2KOH ; 
2K,Co(CN)e  +  2Br  -=  2K3Co(CN)«  +  2KBr. 


60 

5.  NaOH  or  KOH  added  to  a  solution  of  a  cobaltous 
salt,  followed  by  the  addition  of  bromine  water,  precipitates 
on  boiling  the  liquid  (conversion  of  the  cobaltous  ion  Co  *  ' 
into  the  cobaltic  ion  Co  "  *)  brownish-black  Co(OH)3,  cobaltic 
hydroxide,  insoluble  in  a  mixture  of  ammonium  hydroxide 
and  ammonium  chloride : 

2Br  +  2KOH  =  KBr  +  KBrO  +  Ufi  ; 
KBrO  -f-  2Co(OH)2  +  Hp  -  2Co(OH)3  +  KBr. 

6.  KNO2,  potassium  nitrite,  added  in  excess  to  a  solution 
of  a  neutral  salt  of  cobalt,  to  which  sufficient  acetic  acid  lias 
previously  been  added,  produces,  in  concentrated  solutions 
immediately  and  in  dilute  solutions  slowly,  a  yellow  crystal- 
line precipitate  of  K3Co(N02)6,  potassium  cobaltic  nitrite,  a 
combination  of  the  complex  ion  Co(N02)6  with  K3 : 

C0CI2  +  7KNO2  +  2HC2H3O2  =  K3Co(N02)6  +  2KC2H3O2 
+  2KC1  +  NO  +  H2O. 
The  presence  of  free  acetic  acid  is  necessary  to  liberate  the 
nitrous  acid  (required  in  the  oxidation  in  the  transforming  of 
Co  * '  into  Co  * '  *)  from  the  potassium  nitrite.  Free  hydro- 
chloric acid  must  not  be  present ;  in  case  of  its  presence  in 
the  solution,  it  should  be  neutralized  by  the  addition  of 
NaCgHgOg,  sodium  acetate,  previous  to  the  addition  of  the 
acetic  acid  (NaC2H302 -f  HCl  =  NaCl  +  HC2H3O2).  To 
insure  complete  precipitation  of  the  cobalt,  particularly  in 
the  case  of  dilute  solutions,  the  solution  should  be  allowed  to 
stand  in  a  warm  place  for  about  twenty-four  hours. 

7.  Compounds  of  cobalt,  ignited  with  sodium  carbonate  in 
the  reducing  flame  on  charcoal,  yield  dark  metallic,  magnetic 
spangles. 

8.  Compounds  of  cobalt,  fused  in  a  bead  of  borax  or  of 
raicrocosmic  salt  in  either  the  reducing  or  the  oxidizing 
flame,  impart  to  the  bead  a  beautiful  sapphire-blue  color. 


61 

NICKEL,  Ni. 
Atomic  weight,  58.7  (58.3);  valence,  II. 

Silver-white  metal ;  specific  gravity,  8.9. 

NiSO^,  nickelous  sulphate ^  or  NiCl^,  niekelous  chlonde,  may 
be  employed  in  making  the  tests. 

1.  (NH4)2S  precipitates  black  NiS,  nickelous  sulphide,  sol- 
uble in  excess  of  ammonium  sulphide  (particularly  in  the 
presence  of  ammonia),  imparting  a  brownish  color  to  the 
solution.  On  boiling  the  ammonium  sulphide  solution  of 
nickelous  sulphide,  it  undergoes  decomposition  (particularly 
after  the  addition  of  acetic  acid),  with  the  separation  of  the 
previously  dissolved  nickelous  sulphide.  The  precipitate  is 
insoluble  in  dilute  hydrochloric  acid,  but  soluble  in  nitro- 
hydrochloric  acid. 

2.  NaOH  or  KOH  precipitates  amorphous,  apple-green 
Ni(OH)2,  nickelous  hydroxide,  insoluble  in  an  excess  of  the 
reagent. 

3.  NH4OH,  added  in  small  quantity,  precipitates,  in  neu- 
tral solutions  of  nickelous  salts  free  from  ammonium  salts, 
apple-green  Ni(OH)2,  nickelous  hydroxide,  soluble  in  excess 
of  ammonium  hydroxide,  imparting  a  bluish  color  to  the 
solution  in  consequence  of  the  formation  of  complex  coni- 
pounds  of  the  nickel  ammonia  cation. 

4.  NaOH  or  KOH,  added  with  bromine  water  and  the 
liquid  boiled,  precipitates  black  Ni(OH).^,  nickelic  hydroxide, 
(conversion  of  Ni '  *  into  Ni ' ' '),  soluble  in  a  mixture  of 
ammonium  hydroxide  and  ammonium  chloride.  (Compare 
Cobalt,  5,  page  60.) 

5.  KCN,  potassium  cyanide,  precipitates  light-green 
Ni(CN)2,  nickelous  cyanide,  soluble  in  excess  of  the  reagent, 
with  the  formation  of  K2Ni(CN)^,  potassium  nickelous  cyan- 
ide ;  on  the  addition  of  bromine  water  followed  by  j)otassium 

6 


62 

hydroxide   (or   sodium    hydroxide)    to    this   sohition    black 

nickelic  hydroxide  is  precipitated  (distinction  from  cobalt) : 

NiCl^  +  2KCN  =  Ni(CN)2  +  2KC1 ; 

Ni(CN)2  -i-  2KCN  =  K2Ni(CN)4 ; 

2K2Ni(CN),  +  18Br  -t  6NaOH  =  2Ni(OH)3  -f  4KBr  + 

8BrCN  +  6NaBr. 

6.  KNO2,  potassium  nitrite  (under  the  conditions  given 
for  cobalt,  6,  page  60),  fails  to  produce  a  precipitate  in  solu- 
tions of  nickelous  compounds. 

7.  Compounds  of  nickel,  ignited  with  sodium  carbonate 
on  charcoal,  yield  dark  magnetic,  metallic  spangles. 

8.  Compounds  of  nickel,  fused  in  the  oxidizing  flame  in  a 
Dead  of  borax,  yield  a  bead  which  is  purplish  red  while  hot 
and  pale  brownish  yellow  when  cold.  In  the  reducing  flame 
the  bead  becomes  gray  and  opaque,  due  to  the  separation  of 
metallic  nickel. 

Fused  in  a  bead  of  microcosmic  salt  in  the  oxidizing  or 
the  reducing  flame,  salts  of  nickel  yield  a  reddish-brown  bead 
which  becomes  yellow  or  yellowish  red  on  cooling. 


FIFTH    GROUP. 

Metals  precipitated  as  carbonates  (compounds  of  the  diva- 
lent anion  CO3'')  from  neutral  solutions  by  (NH4)2C03, 
ammonium  carbonate :  Barium,  Strontium,  and  Calcium 
(cations  Ba  ' ',  Sr  * ',  Ca  '  *) : 

BaCl^  +  (NH,)2C03  =  BaC03  -f  2NH,C1. 

Complete  precipitation  does  not  take  place  in  solutions 
which  were  originally  acid,  nor  when  ordinary  commercial 
ammonium  carbonate  is  employed,  unless  the  solution  is 
boiled  after  the  addition  of  the  ammonium  carbonate.  Com- 
mercial ammonium  carbonate  consists  of  equal  molecules  of 
NH4HCO3,  acid  ammonium  carbonate,  and  XH2.CO.ONH4, 


63 

ammonium  carbamate.^'^  Dissolving  the  commercial  carbon- 
ate in  water  converts  the  ammonium  carbamate  into  neutral 
ammonium  carbonate : 

NH.HCOg  +  NH2.CO.ONH,  -f  H2O  =  NH.HCOg  + 
(NHJ,C03. 
In  precipitating  with  ammonium  carbonate  containing  acid 
ammonium  carbonate — /.  e.j  the  univalent  anion  HCO3' — 
part  of  the  precipitate  will  consist  of  acid  salts— for  example, 
Ba(HC03)2 — which  are  converted  into  neutral  salts  on 
boiling : 

Ba(HC03)2  =  BaC03  +  CO^  +  H^O. 
The   phosphates  of  the   alkalies  also  precipitate   (as   phos- 
phates) the  members  of  this  group. 

The  solubility,  in  water,  of  some  of  the  compounds  is  as 
follows :  of  the  hydroxides,  barium  hydroxide  is  quite 
soluble,  strontium  hydroxide  is  difficultly  soluble,  calcium 
hydroxide  very  difficultly  soluble.  Of  the  sulphates,  barium 
sulphate  is  practically  insoluble,  strontium  sulphate  fairly 
soluble,  calcium  sulphate  (CaSO^  -|-  2H2O)  quite  soluble. 
In  absolute  alcohol  barium  chloride  and  barium  nitrate  are 
insoluble ;  calcium  chloride  and  calcium  nitrate  are  soluble ; 
strontium  chloride  is  soluble,  but  strontium  nitrate  is 
insoluble. 

BARIUM,  Ba. 
Atomic  weight,  137.4(136.4);  valence,  11. 
Silver-white  metal ;  specific  gravity,  about  4.0. 
BaCl2,  baiium  chloride y  may  be  employed  in  making  the  tests. 
1.   (NH4)2C03,    ammonium    carbonate,    precipitates  white 
flocculent   BaCOg,    barium    carbonate.      The   precipitate   is 


^  According  to  other  views,  commercial  ammonium  carbonate  consists 
of  one  molecule  of  neutral  and  two  molecules  of  acid  ammonium  carbon- 
ate, thus  : 

(NH,)2C03  +  2NH^HC03. 


64 

easily  soluble  in  dilute  hydrochloric  acid,  in  nitric  acid,  and 
in  acetic  acid,  insoluble  in  pure  water,  slightly  soluble  in 
ammonium  chloride,  and,  like  all  the  carbonates  of  the  alka- 
line earths,  soluble  in  water  containing  carbonic  acid. 

2.  H2SO4,  sulphuric  acid,  and  soluble  sulphates,  including 
solutions  of  calcium  and  strontium  sulphates,  precipitate  white, 
finely-pulverulent  BaSO^,  barium  sulphate,  insoluble  in  acids. 
If  the  precipitation  occur  in  a  cold  solution,  the  particles  of 
the  precipitate  are  so  minute  that  they  readily  pass  through  a 
filter ;  whereas,  if  the  precipitation  take  place  in  a  hot  solution, 
and  warm,  dilute  sulphuric  acid  be  employed,  the  precipitate 
formed  is  composed  of  larger  particles  which  are  readily  re- 
tained by  a  filter. 

3.  (NH4)2C204,  ammonium  oxalate,  precipitates  white,  pul- 
verulent BaCaO^  +  H2O,  barium  oxalate  (compound  of  the 
divalent  anion  C2O4''),  wliich  when  freshly  precipitated  is 
soluble  in  acetic  acid  and  in  Hfi./J^,  oxalic  acid. 

4.  Xa2HP04,  sodium  hydrogen  phosphate,  precipitates 
white  flocculent  BaHPO^,  di-basic  barium  phosphate, 
soluble  in  hydrochloric,  nitric,  and  acetic  acids. 

5.  K2Cr04,  potassium  chromate,  produces  in  neutral  or 
acetic  acid  solutions  of  salts  of  barium,  yellow  BaCiO^, 
barium  chromate  (compound  containing  the  chromate  ion 
CrO/'),  soluble  in  hydrochloric  acid  and  in  nitric  acid. 

6.  Compounds  of  barium,  held  in  the  flame  of  a  Bunsen 
burner  by  means  of  a  platinum  wire,  impart  a  yellowish- 
green  color  to  the  flame. 

STRONTIUM,  Sr. 
Atomic  weight,  87.6  (86.94);   valence,  II. 
Yellowish  metal ;  specific  gravity,  2.5. 
Sr(N0^2^  '"fft'ontimn  nitrate^  may  be  employed  in  making  the 
tesU. 

1.  (NHJgCOj,    ammonium    carbonate,    precipitates    white 


65 

SrCOg,  strontium  carbonate,  easily  soluble  in  dilute  hydro- 
chloric acid,  in  nitric  acid,  and  in  acetic  acid. 

2.  H2SO4,  sulphuric  acid,  and  soluble  sulphates,  including 
calcium  sulphate,  precipitate  white,  usually  crystalline  SrSO^, 
strontium  sulphate,  insoluble  in  alcohol.  In  dilute  solutions, 
and  also  on  using  calcium  sulphate  as  the  precipitating  re- 
agent, the  precipitation  takes  place  gradually. 

3.  (NH4)2C204,  ammonium  oxalate,  precipitates  white, 
pulverulent  SrC204(4-  2JH2O),  strontium  oxalate,  soluble 
with  difficulty  in  acetic  acid  and  in  oxalic  acid. 

4.  Na2HP04,  sodium  phosphate,  precipitates  white 
SrHPO^,  di-basic  strontium  phosphate,  soluble  in  hydro- 
chloric, nitric,  and  acetic  acids. 

5.  K2Cr04,  potassium  chromate,  precipitates,  in  not  too 
dilute  solutions  of  strontium,  yellow  SrCrO^,  strontium 
chromate,  soluble  in  hydrochloric  acid  and  in  nitric  acid. 

6.  Compounds  of  strontium  impart  a  crimson  color  to  the 
flame. 

CALCIUM,  Ca. 

Atomic  weig-ht,  40.1  (39.8)  ;  valence,  II. 
Silver- white  metal ;  specific  gravity,  1.57. 
CaCl^,  calcium  chloride^  may  he  employed  in  making  the  tests, 

1.  (NH4)2C03,  ammonium  carbonate,  precipitates  white 
CaCOg,  calcium  carbonate,  easily  soluble  in  dilute  hydro- 
chloric acid,  in  nitric  acid,  and  in  acetic  acid. 

2.  H2SO4  and  soluble  sulpliates  precipitate  immediately,  in 
concentrated  solutions  of  salts  of  calcium,  white,  crystalline 
CaSO^  -f-  2H2O,  calcium  sulphate,  insoluble  in  alcohol,  but 
soluble  in  boiling  hydrochloric  acid.  Precipitation  takes 
place  in  dilute  solutions  either  gradually  or  not  at  all. 

3.  (NH4)2C20^,  ammonium  oxalate,  precipitates  white  pul- 

e  6* 


66 

verulent  CaCgO^  +  II2O  (or  from  dilute  solutions  partly  with 
SllgO),  calcium  oxalate,  easily  soluble  in  hydrochloric  or  in 
nitric  acid,  insoluble  in  acetic  and  oxalic  acids. 

4.  Na^HPO^,  sodium  hydrogen  phosphate,  precipitates 
white  CaHPO^,  di-basic  calcium  phosphate,  soluble  in  hydro- 
chloric, nitric,  and  acetic  acids. 

5.  KgCrO^,  potassium  chromate,  does  not  produce  a  pre- 
cipitate of  CaCr04,  calcium  chromate,  in  dilute  solutions  of 
calcium  salts. 

6.  Compounds  of  calcium  impart  a  yellowish-red  color  to 
the  flame. 


SIXTH  GROUP. 


Bases  not  precipitated  by  any  particular  group  reagent: 
Magnesium,  Potassium,  Sodium,  Ammonium,  and  Lithium 
(cations  Mg  *  * ,  K  * ,  Na  * ,  NH^ ' ,  Li  *). 

The  compounds  of  magnesium,  potassium,  sodium,  ammo- 
nium, and  lithium  are,  in  general,  soluble  in  water.  In 
aqueous  ammonia,  in  addition  to  NH3,  there  is  present  in 
part  NH4OH,  as  evidenced  by  the  fact  that  the  liquid 
changes  red  litmus  to  blue.  Magnesium  (in  the  presence  of 
ammonium  chloride),  potassium,  sodium,  and  lithium  are  not 
precipitated  by  the  group  reagents  HCl,  H2S,  NH4OH, 
(NH,)2S,  and  (NH,).C03. 

MAGNESIUM,  Mg. 
Atomic  weight,  24-. 36  (24-. 18);  valence  II. 

Silver-white  metal;  specific  gravity,  1.75. 

MgSO^y  magnesium  sulphate,  niaij  he  employed  in  making 
the  tests. 

1.  NH4OH  precipitates,  in  neutral  solutions  of  salts  of 
magnesium,  part  of  the  magnesium  as  flocculent  Mg(OH)2, 


67 

magnesium  hydroxide,  leaving  the  other  part  in  sohition  as  a 
double  salt  of  magnesium  and  ammonium — /.  f.,  a  salt  of  the 
complex  ion  Mg(S04)2'' : 

2MgSO.  +  2NH,OH  =  Mg(OH),  +  (NH,),Mg(SO,),. 
This  complex  salt  is  not  decomposed  by  a  slight  excess  of 
ammonium  hydroxide.  Compounds  of  magnesium  are  not 
precipitated  by  ammonium  hydroxide  in  the  presence  of  an 
excess  of  ammonium  chloride,  the  latter  reagent  having  the 
property  of  dissolving  magnesium  hydroxide  : 

Mg(OH)2  +  4NH,C1  =  (NH,),MgCl,  +  2NH,OH. 
This  is  one  explanation  of  the  behavior  of  magnesium  salts 
with  ammonia  and  ammonium  salts !  The  other  explanation  is 
as  follows :  magnesium  hydroxide  is  somewhat,  although  very 
slightly,  soluble  in  water,  and  then  almost  completely  dis- 
sociated in  the  solution.  In  consequence  of  this  constant, 
definite  content  of  hydroxyl  ions  in  the  hydroxide  solution 
magnesium  is  only  partially  precipitated  from  solutions  by 
means  of  the  likewise  only  slightly  dissociated  ammonia  solu- 
tion, which  contains  but  few  hydroxyl  ions ;  ammonium  ions 
are  produced  here  in  considerable  amount,  as  the  result  of 
transpositions  occurring  in  the  liquid,  which  ammonium  ions 
reduce  the  hydroxyl  concentration  below  the  mass  necessary 
for  precipitation.  Ammonia  compared  with  magnesium  hy- 
droxide becomes  a  weaker  base.  Precipitation  does  not  gen- 
erally occur  where,  in  consequence  of  the  addition  of  strongly 
dissociated  ammonium  salts,  ammonium  ions  in  considerable 
amount  were  originally  present. 

2.  NaOH  or  KOH  precipitates,  particularly  on  boiling, 
white  Mg(OH)2,  magnesium  hydroxide. 

3.  NagCOg,  sodium  carbonate,  or  K2CO3,  potassium  car- 
bonate, precipitates  Mg4(C03)3(OH)2,  basic  magnesium  car- 
bonate. (The  carbonic  acid  liberated  in  the  reaction  retains 
part  of  the  magnesium  in  solution  as  an  acid  carbonate ;  this  is 


68 

decomposed  and  precipitated  as  basic  carbonate  by  boiling  the 
solution.)     The  precipitate  is  soluble  in  ammonium  chloride. 

4.  (NH4)2C03  produces  no  precipitate  immediately, 
but  after  stiinding  some  time  a  crystalline  precipitate  of 
MgC03(NH4)2C03  appears.  In  the  presence  of  a  sufficient 
quantity  of  ammonium  chloride  the  precipitation  does  not 
take  place. 

5.  Na^HPO^  produces  in  concentrated  solutions  a  white, 
flocculent  precipitate  of  MgHPO^,  di-basic  magnesium  phos- 
phate. If  ammonium  chloride  and  ammonium  hydroxide 
are  added  to  the  solution  of  the  magnesium  salt,  and  after- 
wards sodium  hydrogen  phosphate  added,  a  white,  crystalline 
precipitate  of  MgNH4P04(-|-  BHgO),  ammonium  magnesium 
phosphate,  a  compound  of  the  trivalent  anion  PO^''',  is  pro- 
duced : 

MgSO,  +  Na^HPO,  +  NH.OH  =  MgNH.PO,  +  Na^SO,  -|- 

The  ammonium  chloride  is  added  to  the  solution  in  order  to 
prevent  the  precipitation  of  the  magnesium  salt  by  the  am- 
monium hydroxide.  The  precipitate  is  always  crystalline; 
in  dilute  solutions  it  forms  gradually,  the  formation  is  facili- 
tated, however,  by  gently  rubbing  the  inner  sides  of  the 
vessel  with  a  glass  rod. 

6.  Compounds  of  magnesium  ignited  on  charcoal  are  some- 
what luminous  in  the  flame.  On  moistening  the  mass  with 
cobaltous  nitrate  and  again  strongly  igniting,  a  pale-pink 
color,  which  is  more  evident  on  cooling,  is  imparted  to  the 


POTASSIUM,   K   (KALIUM). 
Atomic  weight,  39.15  (36.86)  ;  valence,  I. 

Silver-white  metal ;  specific  gravity,  0.87 ;  melting-point, 
62.5°  C. 

KNO^j  potassium  nitrate,  or  KCl,  potassium  chloride,  may 
he  employed  in  making  the  tests. 

1.  PtCl4,  platinic  chloride,  or  a  solution  of  the  same  con- 
taining hydrochloric  acid,  forming  HgPtClg,  hydrochlorpla- 
tinic  acid,  precipitates  from  neutral  or  acid  solutions  yellow 
crystalline  K^PtClg,  potassium  chlorplatinate,  slightly  solu- 
ble in  water,  insoluble  in  alcohol : 

H.PtClg  +  2KC1  =  K^PtClg  +  2HC1 
(a  combination  of  the  anion  PtClg"  with  two  cations  of  K*). 
The  test  is  best  made  in  a  watch-glass,  and  the  liquid 
should  be  stirred  Avith  a  glass  rod.  In  dilute  solutions  the 
precipitate  forms  slowly.  The  addition  of  a  little  alcohol 
and,  if  the  potassium  salt  is  not  a  chloride,  a  drop  of  hydro- 
chloric acid  facilitates  the  precipitation. 

2.  NaHC^H^Og,  acid  sodium  tartrate,  produces,  in  rather 
concentrated  neutral  solutions  of  salts  of  potassium,  a  white, 
granular,  crystalline  precipitate  of  KHC^H^O^,  acid  potas- 
sium tartrate  (a  combination  of  the  univalent  anion  HQH^Og' 
with  the  cation  K  *).  Stirring  the  liquid  with  a  glass  rod  or 
the  addition  of  alcohol  promotes  the  precipitation.  If  the  po- 
tassium solution  has  an  alkaline  reaction,  it  must  be  neutral- 
ized with  acetic  acid  previous  to  the  addition  of  the  acid  so- 
dium tartrate.  H2C4H40g,  tartaric  acid,  may  be  used  instead 
of  acid  sodium  tartrate,  but  in  using  it  NaCgHsOg,  sodium 
acetate,  must  be  added  to  the  solution  : 

KNO3  -f  H2C4HA  +  XaQHA  =  KHC4HA  +  NaNOa  + 

HC2H3O2. 


70 

In  dilute  solutions  of  potassium  salts  precipitation  occurs 
only  after  standing  some  time. 

3.  Sodium  cobaltic  nitrite^'^  produces  immediately  in  con- 
centrated solutions  of  potassium  salts  a  yellow  crystalline 
precipitate  of  K3Co(N02)6,  potassium  cobaltic  nitrite  (a  com- 
bination of  the  complex  anion  Co(N02)/"  with  3K'  cations) : 

(NaNO^).  +  Co(N02)3  +  3KC1  -  Kfio(NO,\  -f  3NaCl  -f 
G  — 3)NaN02. 

4.  Compounds  of  potassium  impart  to  the  flame  a  violet 
color. 

SODIUM,   Na  (NATRIUM). 
Atomic  weight,  23. 05  (22.88);  valence,  I. 

Silver-white  metal ;  specific  gravity,  0.97  ;  melting-point, 
95.6°  C. 

NaCl,  sodium  chlomde,  may  be  efinployed  in  making  the  tests. 

1.  K2H2Sb207,  acid  potassium  pyroantimonate/^^  produces, 
in  neutral  or  slightly  alkaline  concentrated  solutions  of  salts 
of  sodium,  a  white  crystalline  precipitate  of  Na2H2Sb207 
(+  6H2O),  acid  sodium  pyroantimonate  (a  combination  of  the 
anion  H2Sb207''  with  2Na*  cations).  In  dilute  solutions  the 
precipitate  forms  only  after  the  liquid  has  been  standing  some 
time.  Gently  rubbing  the  inner  sides  of  the  vessel  with  the 
part  of  a  glass  rod  over  which  is  slipped  a  piece  of  caout- 
chouc tubing  facilitates  the  formation  of  the  precipitate.  If 
the  sodium  solution  have  an  acid  reaction,  it  should  be  neu- 
tralized with  potassium  carbonate  before  the  addition  of  the 
potassium  pyroantimonate.      Metals   other  than   sodium  or 

*  Prepared  by  treating  a  solution  of  sodium  nitrite  of  about  10  per  cent, 
strength  with  some  cobalt(»us  chloride  and  some  acetic  acid. 

2  The  solution  of  acid  potassium  pyroantimonate  may  be  prepared  by 
boiling  for  a  short  time  1  gram  of  the  salt  with  200  c.c.  of  water,  allow- 
ing  the  liquid  to  cool  and  then  filtering. 


71 

potassium  should  not  be  present,  as  they  interfere  by  forming 
insoluble  antimonates. 

2.  PtCl^,  platinic  chloride,  HgPtClg,  hydrochlorplatinic 
acid,  or  HaC^H^O^,  tartaric  acid,  fails  to  produce  a  precipi- 
tate in  solutions  of  salts  of  sodium. 

3.  Compounds  of  sodium  impart  to  the  flame  an  intense 
yellow  color 

AMMONIUM,   NH4. 

The  cation  NH^  in  its  behavior  with  anions  corresponds  to 
potassium  and  sodium.  Another  analogy  between  the  ammo- 
nium ion  and  the  metals  is  the  existence  of  an  ammonium 
amalgam. 

NH^Clj  ammonium  chloridey  may  be  einployed  in  making 
the  tests. 

1.  The  ammonium  salts  (in  combination  with  volatile 
acids)  are  characterized  by  their  complete  volatility  when 
heated  to  high  temperatures ;  ammonium  borate  and  ammo- 
nium phosphate,  however,  on  being  strongly  heated  leave  a 
residue  respectively  of  boric  acid  and  of  phosphoric  acid. 

2.  PtCl4,  platinic  chloride,  or  a  solution  of  the  same  con- 
taining hydrochloric  acid,  forming  HgPtCle,  hydrochlorplatinic 
acid,  precipitates  in  concentrated  solutions  yellow  crystalline 
(octahedra)  (NH4)2PtClg,  ammonium  chlorplatinate,  slightly 
soluble  in  water,  insoluble  in  alcohol.  The  test  is  best  made 
in  a  watch-glass,  stirring  the  liquid  with  a  glass  rod.  The 
addition  of  a  little  alcohol  and,  if  the  ammonium  salt  is  not 
a  chloride,  a  drop  of  hydrochloric  acid  hastens  the  formation 
of  the  precipitate. 

3.  NaOH  or  KOH  added  to  a  solution  of  a  salt  of  am- 
monium liberates  ammoniacal  gas,  on  boiling  the  solution, 
w^hich  may  be  detected  by  its  odor;  by  its  producing  white 
clouds  of  ammonium  acetate  when  a  glass  rod  wet  with  acetic 


72 

acid  is  held  above  the  liquid ;  by  its  action  upon  turmeric 
paper  moistened  with  water,  which  becomes  brown  when  held 
above  the  liquid  in  which  the  liberation  has  occurred ;  and 
by  its  action  upon  filter  paper  moistened  with  mercurous 
nitrate,  which  becomes  black  when  held  in  the  evolved  gas 
(due  to  the  formation  of  black  NHaHggNOg. 

4.  HgC^H^Og,  tartaric  acid,  or  NaHC^H^Og,  acid  sodium 
tartrate,  produces  in  concentrated  solutions  of  ammonium  salts 
white,  crystalline  ISTH^HC^H^Og,  acid  ammonium  tartrate. 

5.  Sodium  cobaltic  nitrite  produces  a  precipitate  similar 
to  the  one  produced  in  solutions  of  potassium  salts,  but  the 
reaction  is  less  delicate.  (For  conditions  favoring  precipita- 
tion see  Potassium,  3,  page  70.) 

LITHIUM,   Li. 
Atomic  weight,  7.03  (6.98);  valence,  I. 

Silver- white  metal ;  specific  gravity,  0.59  ;  melting-point, 
180°  C. 

LiCl,  lithium  chloride^  may  be  employed  in  making  the  tests. 

1.  Na-jCOg  precipitates,  in  cold  concentrated  solutions  of 
salts  of  lithium,  white  Li2C03,  lithium  carbonate. 

2.  NagHPO^  added  to  a  concentrated  solution  of  a  salt  of 
lithium  produces  a  white,  crystalline  precipitate  of  LigPO^, 
lithium  phosphate. 

3.  Compounds  of  lithium  impart  to  the  flame  a  carmine- 
red  color. 


II.  PROPERTIES  OF  THE  ACIDS. 


FIRST  GROUP. 


Acids  which  are  precipitated  by  BaClj,  barium  chloride, 
from  neutral  and  from  acid  solutions :  Sulphuric  Acid, 
Hydrofluosilicic  Acid. 

SULPHURIC  ACID,   H^SO^. 

(Sulphuric  acid  combines  with  bases  to  form  salts  called 
sulphates.) 

MgSO^j  magnesium  sulphate,  may  be  employed  in  making 
the  tests. 

1.  The  neutral  sulphates  (compounds  of  the  anion  SO^''), 
with  the  exception  of  barium,  strontium,  calcium,  and  lead 
sulphates,  are  easily  soluble  in  water.  Basic  sulphates  of  the 
heavy  metals  are  soluble  in  hydrochloric  acid  or  in  nitric 
acid.  Lead  sulphate  and  the  sulphates  of  the  alkaline  earths 
are  decomposed  and  converted  into  carbonates  by  sodium  or 
potassium  carbonate. 

2.  BaClg,  barium  chloride,  precipitates,  from  solutions  con- 
taining sulphates  or  free  sulphuric  acid,  white,  pulverulent 
BaS04,  insoluble  in  acids.  If  the  precipitation  occur  in  a  cold 
solution,  the  particles  of  precipitate  are  so  minute  that  they 
readily  pass  through  a  filter ;  whereas,  if  the  precipitation  take 
place  in  a  hot  dilute  solution,  the  precipitate  formed  is  com- 
posed of  larger  particles  which  are  readily  retained  by  a  filter. 

3.  Pb(C2H302)2,  plumbic  acetate,  precipitates  white  PbS04, 
plumbic  sulphate,  insoluble  in  dilute  acetic  acid,  somewhat 
soluble  in  boiling  concentrated  acids.  Plumbic  sulphate  is 
easily  soluble  in  (NH4)2C4H406,  ammonium  tartrate;    from 

D  7  73 


74 

this  solution    potassium    cliromate    precipitates    the  lead  as 
yellow  PbCr04,  plumbic  chromate. 

4.  Sulphates,  fused  with  sodium  carbonate  on  charcoal, 
yield  a  residue  containing  NagS,  sodium  sulpliide.  On 
placing  a  portion  of  the  mass  on  a  clean  silver  coin  and 
adding  a  few  drops  of  water,  a  brownish  or  black  stain  of 
Ag2S  is  produced : 

Na^SO,  +  4C  =  ]Sra,S  +  4CO  ; 

Na2S  +  Ag2  +  2H2O  =  Ag,8  -]-  2NaOH  +  H^. 

HYDROFLUOSILIC    ACID,    H2SiF6. 

(Hydrofluosilic  acid  combines  with  bases  to  form  salts 
called  silicofluorides.) 

JVcfg'S'ii^g,  sodium  silicofluorides  may  be  employed  in  making 
the  tests. 

1.  Most  of  the  silicofluorides  (compounds  of  the  complex 
anion  SiF^")  are  sokible  in  water;  when  gently  heated  with 
concentrated  sulphuric  acid  they  evolve  gaseous  SiF^,  silicon 
fluoride,  and  HF,  hydrofluoric  acid  : 

K^SiFg  +  H2SO,  -:  SiF,  -f  2HF  +  K^SO,. 
If  a  piece  of  platinum  foil  containing  a  drop  of  water  be 
inverted  over  the  vessel  in  which  the  decomposition  is  eflected, 
the  water  becomes  milky  in  appearance,  due  to  the  formation 
of  insoluble  HgSiOg,  silicic  acid  : 

3H2O  +  3SiF,  =  H^SiOg  +  2H2SiF6. 

2.  BaClj,  barium  chloride,  precipitates,  in  solutions  of 
hydrofluosilicic  acid  and  of  silicofluorides,  crystalline  BaSiFg, 
barium  silicofluoride,  insoluble  in  dilute  acids. 

3.  KXO3,  potassium  nitrate,  precipitates,  in  solutions  that 
are  not  too  dilute,  translucent,  gelatinous  KgSiFg,  potassium 
silicofluoride,  soluble  with  difficulty  in  water,  insoluble  in 
alcohol. 


75 


4.  NH^OH    produces    NH4F,    ammonium    fluoride,    and 
£[28103,  silicic  acid,  both  of  which  are  precipitated : 
6NH,OH  +  H,SiF6  =  H^SiO^  +  6NH,F  -f-  SH^O. 


SECOND   GROUP. 


Acids  which  are  precipitated  by  BaCla,  barium  chloride,  in 
neutral  solutions,  the  barium  salts  of  which  are  soluble  in 
hydrochloric  acid :  Sulphurous  Acid,  Hypo  sulphurous  Acid, 
Phosphoric  Acid,  Boric  Acid,  Hydrofluoric  Acid,  Carbonic 
Acid,  Silicic  Acid,  Chromic  Acid,  Arsenic  Acid,  Arsenious 
Acid. 

SULPHUROUS  ACID,   HjSOg. 

(Sulphurous  acid  combines  with  bases  to  form  salts  called 
sulphites.) 

iVag^S'Og,  sodium  sulphite,  may  be  employed  in  making  the  tests. 

1.  Of  the  neutral  sulphites  (compounds  of  the  anion  SO./'), 
only  those  of  the  alkalies  are  soluble  in  water ;  the  others  are 
easily  soluble  in  acids,  with  the  evolution  of  SO2,  sulphurous 
anhydride  : 

BaSOa  +  2HC1  =  BaCl^  +  SO^  i-  Hfi. 

2.  Dilute  acids  decompose  sulphites,  with  the  evolution  of 
SO2,  sulphurous  anhydride,  which  may  be  recognized  by  its 
odor  (that  of  burning  sulphur).  The  presence  of  sulphurous 
anhydride  may  be  detected  in  gaseous  mixtures  by  its  be- 
havior with  KIO3,  potassium  iodate.  A  piece  of  filter  paj>er 
saturated  with  a  solution  of  potassium  iodate  and  starch  paste, 
brought  while  wet  in  contact  with  gaseous  mixtures  contain- 
ing sulphurous  anhydride,  becomes  blue  in  color,  owing  to 
the  reduction  of  HIO3,  iodic  acid,  to  iodine,  and  the  action 
of  the  latter  on  the  starch.      Bv  means  of  the  sulphurous 


76 

anhydride,  in  the  presence  of  water,  the  iodic  acid  is  reduced 
to  HI,  hydriodic  acid  (transformation  of  IO3'  to  I'). 
3SO2  +  3H2O  +  HIO3  =  HI  +  3H2SO,. 
The  hydriodic  acid,  by  the  action   of  the  remaining  iodic 
acid,  is  reduced,  with  the  liberation  of  free  iodine : 

SHI  4-  HIO3  =  I,+  SHp. 
(As  the  free  iodine  is  reconverted  by  an  excess  of  sulphurous 
anhydride  into  hydriodic  acid  : 

.  I2  +  SO2  +  2H2O  =  2HI  +  H2SO,, 
an  excess  of  the  sulphurous  anhydride  causes  a  disappearance 
of  the  color.) 

3.  BaClg  precipitates  white  BaSOg,  barium  sulphite,  soluble 
in  acids. 

4.  Pb(C2H302)2  precipitates  white  PbS03,  plumbic  sulphite, 
soluble  in  nitric  acid. 

5.  AgN03,  argentic  nitrate,  precipitates  white  AggSOg, 
argentic  sulphite,  soluble  in  nitric  acid.  On  boiling  the 
precipitate  with  water,  it  is  decomposed  into  metallic  silver 
and  sulphuric  acid,  the  liquid  becoming  gray  in  color,  due 
to  the  separated  metallic  silver : 

Ag,SO,  +  H,0  =  Ag,  +  H,SO.. 

6.  ZnSO^,  zinc  sulphate  solution,  containing  a  little 
Na2NOFe(CN)5,  sodium  nitroprusside,  added  to  a  solution 
of  a  sulphite  which,  if  not  neutral,  has  been  neutralized 
with  acetic  acid,  produces  a  red  coloration ;  or  a  flocculent, 
purplish-red  precipitate,  if  the  -solution  contain  a  considerable 
quantity  of  the  sulphite.  When  operating  with  dilute  solu- 
tions of  a  sulphite,  the  test  may  be  made  more  delicate  by 
the  addition  of  a  few  drops  of  potassium  ferrocyanide  solu- 
tion.    (Distinction  from  hyposulphites.) 

7.  HgS  conducted  into  a  solution  of  sulphurous  acid  de- 
composes the  latter,  with  the  separation  of  sulphur  and  the 
probable  formation  of  HgSgOg,  pentathionic  acid  : 

5SO2  +  5H2S  =  H^SA  +  S, -f  4H2O. 


77 

8.  Sulpliites  ignited  with  sodium  carbonate  on  charcoal 
yield  a  yellowish  residue  containing  sodium  sulphide,  as  in 
the  case  of  sulphates.  A  portion  of  the  residue  placed  on  a 
clean  silver  coin  and  moistened  with  a  few  drops  of  water  pro- 
duces a  brown  or  black  stain  of  argentic  sulphide  on  the  coin. 

HYPOSULPHUROUS    ACID,    HjSjOg    (THIOSULPHURIC 

ACID). 

(Hyposulphurous  or  thiosulphuric  acid  combines  with  bases 
:o  form  salts  called  hyposulphites  or  thiosulphates.) 

Na^S^O^j  sodium  hyposulphite^  may  be  employed  in  making 
the  tests. 

1.  Most  of  the  liyposulphites  (thiosulphates)  (compounds 
of  the  anion  8203^')  are  soluble  in  water. 

2.  HCl  or  H2SO4  added  to  a  solution  of  a  hyposulphite 
liberates  HgSgOg,  hyposulphurous  acid,  which  quickly  breaks 
up  into  sulphur,  sulphurous  anhydride,  and  water : 

Na,SA  +  2HC1  =  H2SA  +  2NaCl ; 

H2S2O3  =  SO2  +  S  +  H2O. 
Thus  hyposulphites,  on  the  addition  of  either  of  the  above 
acids,  are  decomposed  and  yield  sulphurous  anhydride,  which 
may  be  recognized  by  its  odor,  and  free  sulphur. 

3.  BaCl2,  barium  chloride,  produces  in  concentrated  solu- 
tions of  hyposulphites  a  white  precipitate  of  BaSgOg,  barium 
hyposulphite,  soluble  in  a  large  quantity  of  water.  It  is  also 
soluble  in  hydrochloric  acid,  with  the  evolution  of  sulphurous 
anhydride  and  the  separation  of  sulphur. 

4.  Pb(C2H302)2,  plumbic  acetate,  precipitates  white  PbSgOjj, 
plumbic  hyposulphite,  soluble  in  nitric  acid. 

5.  AgNOg,  argentic  nitrate,  precipitates  white  Ag2S203, 
argentic  hyposulphite,  soluble  in  excess  of  sodium  hyposul- 
phite solution  : 

Ag2S203  +  Xa2S203  =  2NaAgS203. 


78 

The  precipitiite  becomes  almost  immediately  yellow,  then 
brown,  and  finally  black,  due  to  the  formation  of  argentic 
sulphide : 

Ag^S  A  +  HP  =  Ag,S  +  H^SO,. 

6.  FeCla,  ferric  chloride,  immediately  colors  hyposulphite 
solutions  reddish  violet.     (Distinction  from  sulphites.) 

7.  Hyposulphites  ignited  with  sodium  carbonate  on  char- 
coal yield  a  residue  containing  sodium  sulphide,  as  in  the 
case  of  sulphates  and  of  sulphites.  A  portion  of  the  residue 
placed  on  a  clean  silver  coin  and  moistened  with  water  pro- 
duces a  brown  or  black  stain  of  argentic  sulphide. 

PHOSPHORIC    ACID,    HgPO^. 

(Phosphoric  acid  combines  with  bases  to  form  salts  called 
phosphates.) 

Na^HPO^^  sodium  hydrogen  phosphate ,  may  he  employed  in 
making  the  tests. 

1.  The  phosphates  of  the  alkalies  (compounds  of  the  anions 
PO/'^  HPO/^  and  H^PO/)  are  soluble  in  water;  the  phos- 
phates of  other  metals  are  soluble  in  acids. 

2.  BaClg,  barium  chloride,  precipitates  in  solutions  of  the 
neutral  phosphates  white  BaHPO^  or  Ba3(P04)2,  soluble  in 
hydrochloric  acid  or  in  nitric  acid. 

3.  Pb(C2H302)2,  plumbic  acetate,  precipitates  white 
Pb3(P04)2,  soluble  in  nitric  acid. 

4.  AgNOg,  argentic  nitrate,  produces  in  solutions  of  the 
phosphates  a  light-yellow  precipitate  of  AggPO^,  soluble  in 
nitric  acid  and  in  ammonium  hydroxide. 

5.  NH4CI,  ammonium  chloride,  NH^OH,  ammonium  hy- 
droxide, and  MgS04,  magnesium  sulphate,^^>  added  in  turn  to 
a  solution  of  a  phosphate,  produce  a  white,  crystalline  pre- 


»  The  three  reagents  composing  the  so-called  "magnesia  mixture." 


79 

cipitate   of    MgNHjPO^  +  BHgO,    ammonium    magnesium 
phoaphate : 

NaaHPO^  +  NH.OH  +  MgSO,  =  MgNH.PO,  + 
Na,SO,  +  Hp. 
(The  ammonium  chloride  is  added  to  prevent  the  precipitation 
of  the  magnesium  as  magnesium  hydroxide  by  the  ammo- 
nium hydroxide.)  The  precipitate  is  sparingly  soluble  in 
pure  water,  and  very  slightly  soluble  in  water  containing 
ammonium  hydroxide.  In  precipitating  very  dilute  solu- 
tions the  precipitate  forms  more  rapidly  when  the  inner  sides 
of  the  vessel  are  gently  rubbed  with  a  glass  rod. 

6.  NH4HM0O4,  ammonium  molybdate,  added  in  excess, 
with  a  considerable  quantity  of  nitric  acid,  to  a  solution  of 
phosphoric  acid  or  a  phosphate,  produces  a  yellow  precipitate, 
probably  of  (NH4)3P04(Mo03)i2,  ammonium  phospho- 
molybdate,  a  compound  containing  the  complex  anion 
PO,(Mo03),/'^ 
12NH,HMoO,  +  H3PO,+  9HN03=  (NHj3PO,(Mo03),3  + 

9NH4N03-fl2H20. 
The  precipitate  is  insoluble  in  dilute  nitric  acid,  but  easily 
soluble  in  ammonium  hydroxide;  it  is  reprecipitated  from 
the  ammoniacal  solution  by  the  addition  of  excess  of  nitric 
acid.  The  precipitate  is  also  soluble  in  excess  of  a  phosphate, 
and  thus  is  explained  the  non-appearance  of  a  precipitate 
when  only  a  little  ammonium  molybdate  is  added  to  a  solu- 
tion containing  much  phosphoric  acid.  In  dilute  solutions 
the  precipitate  forms  slowly.  The  precipitation  is  hastened 
by  warming  the  solution  to  a  temperature  of  40°  C  A 
higher  temperature  should  be  avoided. 

(Pyrophosphates  (compounds  of  the  anion  PgO;'"')  yield 
with  argentic  nitrate  white  precipitates  of  Ag4P20-,  argentic 
pyrophosphate.  Metaphosphates  (compounds  containing  the 
anion  PO3' — /.  e.,  n(P03') )  likewise  yield  white  precipitates 


80 

of  AgPOg.  Only  the  metaphosphates  coagulate  albumin. 
Sodium  pyrophosphate  may  be  obtained  by  strongly  heating 
disodium  phosphate : 

'iNa^HPO^  =  Na.P^O,  +  Hfi. 
Sodium  metaphosphate  may  be  produced  by  strongly  heating 
sodium  ammonium  hydrogen  phosphate  : 

NaNH.HFO^  -  NaPOa  +  NH3  +  H^O.) 

BORIC  ACID,  H3BO3. 

(Boric  acid  combines  with  bases  to  form  salts  called 
borates.) 

Na^B^O^,  sodium  biborate  (borax),  may  be  employed  in 
making  the  tests. 

1.  Of  the  borates  (compounds  containing  various  anions — 
for  example,  BO/,  BO3''',  and  B,0/'),  those  of  the  alkalies 
are  easily  soluble  in  water.  On  treating  warm  concentrated 
solutions  of  borates  with  acids,  colorless  scales  of  boric  acid 
slowly  separate.     Boric  acid  volatilizes  with  steam. 

2.  BaClg,  barium  chloride,  produces  in  concentrated  solu- 
tions of  borates  white  Ba(B02)2,  barium  metaborate,  easily 
soluble  in  excess  of  barium  chloride  and  in  ammonium  chlo- 
ride : 

^a^Bfi,  +  2BaCl2  +  H2O  -=  2Ba(B02)2  +  2NaCl  +  2HC1. 

3.  Pb(C2H302)2,  plumbic  acetate,  precipitates  in  concen- 
trated solutions  white  Pb(B02)2,  lead  metaborate,  soluble  in 
excess  of  the  reagent. 

4.  AgNOg,  argentic  nitrate,  precipitates  in  concentrated 
solutions  of  neutral  borates  white  AgBOg  +  JH2O,  argentic 
metaborate,  which  is  occasionally  tinged  with  yellow,  due  to 
the  presence  of  argentic  oxide.  In  solutions  of  acid  borates 
the  precipitate  is  AggBgO,5.  Both  precipitates  are  easily 
soluble  in  nitric  acid.     By  continued  washing,  and  readily  by 


81 

Ixiiling  with  water,  both  precipitates  are  decomposed  into 
soUible  boric  acid  and  brown  argentic  oxide ;  in  dilute  sohi- 
tions  a  brown  precipitate  of  argentic  oxide  is  directly  pro- 
duced. 

5.  Boric  acid,  in  the  powdered  condition,  placed  in  a  porce- 
lain dish  and  covered  with  alcohol  gives  a  greenish  flame  on 
igniting  the  alcohol.  Borates,  in  the  powdered  condition, 
impart  the  same  greenish  color  to  the  flame,  but  must  be 
moistened  with  a  few  drops  of  concentrated  sulphuric  acid 
before  the  addition  of  the  alcohol.  The  greenish  color  im- 
parted to  the  flame  is  due  to  (C2H5)3B03,  the  ethyl  ester  of 
boric  acid,  formed  in  the  reaction.  Boric  acid  (without  the 
addition  of  alcohol)  when  strongly  heated  on  platinum  wire 
imparts  a  greenish  color  to  the  flame.  (Compounds  of  barium 
and  of  copper  and  compounds  containing  chlorine  interfere 
with  the  test.) 

6.  Turmeric  paper  dipped  in  an  aqueous  solution  of  boric 
acid,  or  in  a  solution  of  a  borate  acidified  with  hydrochloric 
acid,  and  warmed  until  dry,  becomes  reddish  brown  in  color. 
On  bringing  dilute  sodium  or  potassium  hydroxide  solution 
in  contact  with  the  reddish-brown  paper,  the  color  becomes 
blue  and  then  greenish  black. 

HYDROFLUORIC  ACID,  HF. 

(Hydrofluoric  acid  combines  with  bases  to  form  salts  called 
fluorides.) 

KF,  potassium  fluoride,  or  NaF,  sodium  fluoride,  may  he 
employed  in  making  the  tests. 

1.  Of  the  fluorides  (compounds  of  the  anion   F'),  those 
of  the  alkalies  are  easily  soluble  in  water ;  the  others  are 
soluble  only  with  great  difficulty. 
/ 


82 

2.  BaClg  precipitates  from  solutions  of  fluorides  white 
BaF2,  soluble  in  hydrochloric  acid ;  Pb(C2H302)2  precipitates 
white  PbFg,  easily  soluble  in  nitric  acid ;  and  AgNOg  pre- 
cipitates white  AgF,  also  easily  soluble  in  water. 

3.  CaCl2,  calcium  chloride,  precipitates  white,  gelatinous 
CaFg,  calcium  fluoride,  almost  insoluble  in  water,  soluble  with 
difficulty  in  mineral  acids. 

4.  Hydrofluoric  acid  has  the  property  of  etching  glass, 
forming  with  the  silicic  oxide  of  the  glass  volatile  SiF^,  silicon 

fluoride : 

Si02  +  4HF  =  SiF,  +  2H2O. 

The  test  is  performed  in  a  platinum  crucible  covered  with  a 
watch-glass.  The  convex  side  of  the  watch-glass  is  covered 
with  melted  wax,  and,  after  the  wax  has  cooled,  a  design 
or  figure  is,  by  means  of  a  sharpened  piece  of  wood  or  the 
point  of  a  knife-blade,  graven  of  sufficient  depth  in  the  wax 
to  expose  an  uncoated  surface  of  glass.  The  pulverized 
fluoride  is  placed  in  the  crucible,  moistened  with  concen- 
trated sulphuric  acid,  quickly  covered  with  the  watch-glass 
(waxed  side  down),  and  the  whole  placed  on  a  moderately 
warm  iron  plate  or  porcelain  dish.^'^  After  some  time  the 
watch-glass  is  taken  from  the  crucible,  and  when  the  wax 
is  removed  the  graven  design  will  appear  etched  in  the 
glass. 

5.  In  decomposing  fluorides  containing  considerable  silicic 
acid  with  concentrated  sulphuric  acid,  gaseous  SiF^  is  evolved, 
which,  when  conducted  through  a  glass  tube  moistened  with 
water,  undergoes  decomposition,  rendering  the  water  turbid, 
with  the  deposition  of  silicic  acid  : 

3SiF,  +  3H2O  =  H^SiOs  -\-  2il^iF,. 


I  The  watch-glass  should  be  filled  with  cold  water,  to  jjrevent  the  melt- 
ing of  the  wax. 


83 

The  result  of  the  reaction  is  especially  observable  on  drying 
the  tube. 


CARBONIC  ACID,  HjCO,. 

(Carbonic  acid  combines  with  bases  to  form  salts  called  car- 
bonates.) 

Na^CO^y  sodium  carbonate j  may  be  employed  in  making  the 


1.  The  carbonates  (compounds  of  the  anion  CO3'')  of  the 
alkalies  are  soluble  in  water ;  the  other  carbonates  are  insolu- 
ble in  water.  Many  of  the  latter  are,  however,  soluble  in 
water  containing  carbon  dioxide,  forming  acid  carbonates 
(compounds  of  the  anion  HCO3) : 

CaCOs  +  CO2  +  H,0  =  Ca(HC03)2. 
Carbonates  in  general  readily  dissolve  in  dilute  acids,  with 
effervescence  (due  to  the  liberation  of  carbon  dioxide).     The 
metal  of  the  carbonate  forms  a  salt  with  the  acid  used  as  a 
solvent : 

BaCOg  4-  2HC1  =-  BaCla  +  CO2  +  H^. 

2.  HCl  or  any  dilute  acid  (except  hydrocyanic  acid),  added 
to  a  carbonate  either  in  solution  or  in  the  solid  condition,^^^ 
produces  effervescence,  due  to  the  evolution  of  carbon  dioxide. 
The  latter  may  be  detected  by  inclining  the  test-tube  in  which 
the  effervescence  has  taken  place  so  as  to  pour  only  the  gas- 
eous CO2  into  another  test-tube  containing  clear  calcium  hy- 
droxide solution.  The  CO2,  being  specifically  heavier  than 
air,  displaces  the  air  in  the  tube  containing  calcium  hy- 
droxide, and,  on  closing  the  latter  tube  with  the  thumb  and 


1  The  minerals  magnesite  (MgCO,),  dolomite  (CaCOgjMgCOj),  and 
siderite  (FeCOg)  produce  eflfervescence  with  a  dilute  acid  only  after  being 
warmed. 


84 

agitating  the  liquid,  a  turbidity  is  produced,  due  to  the  for- 
mation of  CaCOg,  calcium  carbonate  : 

CO2  +  Ca(OH)2  -  CaCOg  +  H^O. 

3.  BaCla,  barium  chloride,  precipitates  white  BaCOg, 
bariimi  carbonate ;  Pb(C2H302)2,  plumbic  acetate,  precipitates 
white  PbCOa ;  both  are  soluble  with  effervescence  in  dilute 
acids. 

4.  AgNOg,  argentic  nitrate,  precipitates  white  Ag2C03, 
argentic  carbonate,  which  in  a  little  time  becomes  yellowish, 
and  on  being  boiled  with  an  excess  of  sodium  carbonate 
changes  to  brownish-gray  AggO,  argentic  oxide.  The  argen- 
tic oxide  is  soluble  in  ammonium  hydroxide  and  in  ammo- 
nium carbonate. 


SILICIC  ACID,   H^SiOj. 

(Silicic  acid  combines  with  bases  to  form  salts  called  sili- 
cates.) 

Na^SiO^y  sodium  silicate,  may  he  employed  in  making  the  tests. 

1.  Of  the  silicates  (compounds  containing  the  various 
anions  SiO/''^  SiOa'',  Si20/',  etc.),  only  those  of  the  alkalies 
are  soluble  in  water ;  the  others  are  partially  soluble  in  con- 
centrated acids. 

The  addition  of  an  acid  (as  hydrochloric  acid)  to  a  solution 
of  a  silicate  of  an  alkali  causes  the  separation  of  silicic  acid, 
which,  if  the  solution  is  of  sufficient  concentration,  appears  as 
a  gelatinous  precipitate ;  ammonium  chloride  also  separates 
silicic  acid  from  solutions  of  silicates  of  the  alkalies : 
Na^SiOj  +  2HC1  =  H2Si03  +  2NaCl ; 
Na2Si03  +  2NH,C1  +  2H2O  =  H2Si03  +  2NaCl  +  2NH,0H. 
The  silicic  acid  separated  in  this  manner  is  somewhat  soluble 
in  dilute  acids.  On  evaporating  the  solution  containing  silicic 
acid — i.e.y  the  solution  with  the  precipitate  in  suspension — to 


85 

the  dryness  of  dust  on  a  water-bath,  the  silicic  acid  loses 
water  and  amorphous  silicic  acids  are  produced, — i.e.,  poly- 
silicic  acids,  H2Si409,  for  example,  which  are  entirely  insolu- 
ble in  water : 

4H2Si03  =  H^Si  A  -h  3H2O. 
On  extracting  the  residue  with  water  containing  a  little  hy- 
drochloric acid,  the  metal  which  had  originally  been  in  com- 
bination with  the  silicic  acid  is  dissolved  as  a  chloride,  while 
the  silicic  acid  remains  undissolved.  Evaporation  over  a  free 
flame  is  not  advised,  as  thereby  (because  of  the  stability  of 
silicic  acid  when  heated)  a  part  of  the  salt  might  be  recon- 
verted into  silicates,  as,  for  example : 

H^Si  A  +  2NaCl  =  Na^Si  A  +  2HC1. 
For  the  methods  employed  in  dissolving  and  disintegrating 
silicates  insoluble  in  water,  see  Silicates,  page  130. 

2.  BaClg,  barium  chloride,  precipitates  in  solutions  of 
silicates  of  the  alkalies  w^hite  BaSiOg,  barium  silicate; 
Pb(C2H302)2,  plumbic  acetate,  precipitates  white  PbSiOg, 
plumbic  silicate ;  AgNOa,  argentic  nitrate,  precipitates  yellow- 
ish Ag2Si03,  argentic  silicate ;  all  soluble  in  acids,  the  argen- 
tic silicate  being  also  soluble  in  ammonium  hydroxide. 

3.  NH4HM0O4,  ammonium  molybdate,  together  with  an 
excess  of  nitric  acid,  added  to  a  solution  of  a  silicate  pro- 
duces a  yellowish  coloration,  and,  in  the  presence  of  con- 
siderable ammonium  chloride,  a  lemon-yellow  precipitate. 
Warming  facilitates  the  reaction. 

4.  On  fusing  a  silicate  with  microcosmic  salt  in  the  loop  of 
a  platinum  wire,  the  sodium  metaphosphate  which  is  produced 
dissolves  the  base,  while  the  silicic  acid  remains  undissolved 
and  swims  in  small  opaque  particles  in  the  otherwise  trans- 
parent bead  while  the  latter  is  in  a  state  of  fusion  ("  skeleton 
of  silica")  ;  for  example  : 

CaSiOa  +  NaPOg  =  CaNaPO^  +  SiO^. 


86 

Uncombined  silicic  acid  produces  the  same  result.  The  reac- 
tion is  made  more  evident  by  coloring  the  bead  with  a  com- 
pound of  copper  or  of  iron. 

ARSENIOUS  ACID,  H3ASO3.    (See  page  29.) 

ARSENIC  ACID,  HjAsO^.    (See  page  34..) 

CHROMIC    ACID,  HjCrO^. 

(Chromic  acid  combines  with  bases  to  form  salts  called 
chromates.) 

K,firO^^  potassium  chromate,  may  be  employed  in  making 
the  tests. 

1.  Most  of  the  chromates  are  insoluble  in  water.  The 
chromates  (compounds  of  the  anion  CrO^^Q  of  the  alkalies 
(the  neutral  salts)  are  easily  soluble ;  the  dichromates 
(the  so-called  acid  salts,  compounds  containing  the  anion 
CrgOy'')  are  soluble,  with  the  production  of  a  reddish- 
yellow  color. 

2.  BaCla,  barium  chloride,  precipitates  from  solutions  of 
chromates  yellow  BaCrO^,  barium  chromate,  soluble  with 
great  difficulty  in  water,  soluble  in  hydrochloric  and  in  nitric 
acids. 

3.  Pb(C2H302)2,  plumbic  acetate,  precipitates  yellow,  crys- 
talline PbCrO^,  plumbic  chromate  (chrome-yellow),  insoluble 
in  water  and  in  acetic  acid,  soluble  in  nitric  acid  and  in 
sodium  hydroxide,  in  the  latter  with  the  formation  of 
Na2Cr04,  sodium  chromate,  and  NagPbOg,  sodium  plum- 
bite  ;  acetic  acid  reprecipitates  lead  chromate  from  the  sodium 
hydroxide  solution. 

4.  AgNOg,  argentic  nitrate,  precipitates  in  solutions  of 
chromates  purplish-red  AggCrO^,  argentic  chromate,  and  in 
solutions  of  dichromates  purplish-red  Ag2Cr207,  argentic  di- 


87 

chromate,  both  soluble  in  nitric  acid  and  in  ammonium 
hydroxide. 

5.  HgS,  hydrogen  sulphide,  conducted  into  a  solution  of  a 
chromate  containing  considerable  free  hydrochloric  acid  or 
sulphuric  acid,  reduces  the  chromate,  with  the  formation  of 
a  soluble  chromic  salt  and  the  separation  of  sulphur,  the 
solution  at  the  same  time  becoming  green  in  color  (conver- 
sion of  the  anion  Cr04''  into  the  cation  Cr*  * ')  : 

2K2CrO,  +  SH^S  +  lOHCl  --=  2CtC\,  +  S3  -|-  4KC1  +  SHp. 
In  case  the  acid  is  present  in  small  quantity  greenish 
Cr(OH)3,  chromic  hydroxide,  or  (especially  on  warming  the 
solution)  brown  chromium  chromate,  is  precipitated : 

2K2CrO,  +  3H2S  +  4HC1  =  2Cr(OH)3  +  S3  +  4KC1  + 
2H2O; 

SK^CrO,  +  3H2S  +  6HC1  =  (CrO)2CrO,  +  S3  +  6KC1 

+  6H2O. 

The  action  of  ammonium  sulphide  in   neutral  or  alkaline 

solutions  of  chromates  is  similar  to  that  of  hydrogen  sulphide. 

6.  On  adding  C2H5OH,  alcohol,  to  a  solution  of  a  chromate 
or  dichromate  containing  free  hydrochloric  or  sulphuric  acid, 
and  warming  the  liquid,  the  chromate  is  reduced  to  a  chromic 
salt,  while  the  alcohol  is  oxidized  to  CgH^O,  aldehyde ;  in 
consequence,  the  liquid  becomes  green  in  color  and  the  odor 
of  aldehyde  becomes  evident : 

K^CrA  +  4H2SO,  +  SC^H^OH  =  2KCr(SO,)2  +  SC^H.O  + 

7H,0. 

7.  On  heating  a  chromate  with  concentrated  hydrochloric 
acid  chlorine  is  evolved  and  chromic  chloride  is  produced  : 

2K2Cr04  +  16HC1  =  2CrCl3  4-  4KC1  +  SHfl  +  6C1. 

8.  H2O2,  hydrogen  dioxide,  added  in  small  quantity  to 
a  dilute  solution  of  a  chromate,  rendered  acid  with  hydro- 
chloric acid,  produces  a  blue  coloration  in  the  solution  due  to 
the  formation  of  perchroraic  acid  (HCrOg?).     On  agitating 


88 

the  liquid  with  ethyl  ether  the  latter  extracts  the  perchromic 
acid  from  the  water  and  becomes  blue  in  color.  Care  should 
be  taken  not  to  use  an  excess  of  the  chromate,  otherwise  the 
chromic  acid  and  perchromic  acid  will,  with  the  evolution  of 
oxygen,  be  reduced  to  chromic  oxide. 

9.  Chromates  fused  in  a  bead  of  borax  or  of  microcosraic 
salt  impart  a  yellowish-green  color  to  the  bead  while  hot, 
which  becomes  emerald-green  on  cooling.  ' 


THIRD  GROUP. 

Acids  which  are  not  precipitated  by  BaClg,  barium  chloride, 
but  are  precipitated  by  AgN03,  argentic  nitrate  :  Hydrochloric 
Acid,  Hydrobromic  Acid,  Hydriodic  Acid,  Hydrocyanic  Acid, 
Hydroferrocyanic  Acid,  Hydroferricyanic  Acid,  Sulphydric 
Acid  (Hydrog^en  Sulphide),  Nitrous  Acid,  Hypochlorous  Acid. 

HYDROCHLORIC  ACID,  HCI. 

(Hydrochloric  acid  combines  with  bases  to  form  salts  called 
chlorides.) 

NaCl,  sodium  cMoride,  may  be  employed  in  making  the  tests. 

1.  The  chlorides  (compounds  of  the  anion  CI')  are  sol- 
uble in  water,  with  the  exception  of  argentic  chloride, 
mercurous  chloride,  and  plumbic  chloride ;  the  latter,  how- 
ever, being  sparingly  soluble  in  cold  water.  (For  dissolv- 
ing insoluble  chlorides,  see  Dissolving  Oxides  and  Salts, 
page  121.) 

2.  AgN03,  argentic  nitrate,  precipitates  white  curdy  AgCl, 
argentic  chloride,  insoluble  in  dilute  nitric  acid,  easily  soluble 
in  ammonium  hydroxide.  From  its  solution  in  ammonium 
hydroxide    the  argentic  chloride  is  reprecipitated  by  nitric 


89 

acid.  The  precipitate  is  also  soluble  in  KCN,  |X)tassium 
cyanide,  and  in  NagSgOs,  sodium  hyposulphite,  with  the  for- 
mation of  the  complex  anion  AgSaOg' : 

Na^SA  +  AgCl  -:  NaAgSA  +  NaCl. 
When  exposed  to   sunlight  the  precipitate  changes  in   color 
to  violet  and  then  to  black. 

3.  Pb(C2H302)2,  plumbic  acetate,  precipitates,  in  hydro- 
chloric acid  and  in  solutions  of  chlorides,  white,  sometimes 
crystalline  PbCl2,  plumbic  chloride,  sparingly  soluble  in  cold 
water,  easily  soluble  in  hot  water,  from  which,  when  in  con- 
centrated solution,  it  crystallizes,  on  cooling,  in  glistening 
rhombic  needles.  Precipitation  does  not  occur  in  very  dilute 
solutions  of  chlorides. 

4.  On  placing  a  dry  mixture  of  a  chloride  and  potassium 
dichromate  in  a  small  retort  or  tubulated  fractionating  flask, 
adding  concentrated  sulphuric  acid,  and  carefully  distilling 
the  contents  of  the  retort,  Cr02Cl2,  chlorochromic  anhydride, 
as  a  brownish-red  gas,^^^  is  produced,  which,  when  conducted 
into  a  receiving  flask,  condenses  into  a  brownish-red  liquid  : 
4KC1  +  K2Cr207  +  6H2SO,  =  2Cr02Cl2  +  6KHSO,  +  SUfi. 
Sodium  hydroxide  added  to  the  brownish-red  distillate  pro- 
duces a  yellowish  solution  of  NagCrO^,  sodium  chromate^^^ 
(together  with  sodium  chloride) : 

Cr02Cl2  +  4NaOH  =  Na2CrO,  +  2NaCl  -f-  2H2O. 
If  the  yellowish  solution   is  acidified  with  acetic  acid  and 
plumbic  acetate  added,  the  production  of  a  yellow  precipitate 
of  plumbic  chromate  gives  indirect  but  conclusive  evidence  of 
chlorine. 

^  Distinction  from  iodides,  whioh  furnish  violet-colored  vapors  of  free 
iodine. 

2  Distinction  from  bromides,  which  do  not  impart  a  color  to  the  liquid. 

8* 


90 


HYDROBROMIC    ACID,    HBr. 

(Hydrobromic  acid  combines  with  bases  to  form  salts  called 
bromides.) 

KBvj  potassium  bromide^  may  he  employed  in  making  the 
tests. 

1.  The  bromides  (compounds  of  the  anion  Br')  in  general 
are  soluble  in  water.  Argentic  bromide  and  mercurous 
bromide  are  insoluble ;  plumbic  bromide  is  sparingly  soluble 
in  water. 

2.  AgNOg,  argentic  nitrate,  precipitates  yellowish-white, 
curdy  AgBr,  argentic  bromide,  insoluble  in  dilute  nitric  acid, 
sparingly  soluble  in  dilute  and  more  easily  soluble  in  concen- 
trated ammonium  hydroxide.  The  precipitate  is  easily  soluble 
in  potassium  cyanide  and  in  sodium  hyposulphite. 

3.  Pb(C2H302)2,  plumbic  acetate,  precipitates  in  hydro- 
bromic acid  and  in  solutions  of  bromides  white,  crystalline 
PbBrg,  plumbic  bromide,  sparingly  soluble  in  cold  water, 
more  easily  soluble  in  hot  water. 

4.  Dry  bromides,  on  being  distilled  in  a  retort  with  potas- 
sium dichromate  and  concentrated  sulphuric  acid  (see  under 
Chlorides,  4,  page  89),  yield  brown  vapors  of  bromine,  which 
condense  in  the  receiver  as  a  brown  distillate  of  bromine,  free 
from  chromium : 

6KBr  +  K^Cr^Oy  +  TH^SO,  =--  Cr2(SO,)3  -f  4K2SO4  + 

7H2O  -f-  Brg. 
Sodium  hydroxide  added  to  the  distillate  decolorizes  it,  form- 
ing sodium  bromide  and  NaBrO,  sodium  hypobromite  : 

Br2  -f  2NaOH  =  NaBr  -f-  NaBrO  -f-  H^O. 
As  sodium  hypobromite  solution  is  itself  yellowish  in  color, 
it  is  well   finally  to  add  ammonium  hydroxide,  whereupon 
immediate  and  complete  decolorization  will  occur : 

2NH,0H  +  SNaBrO  =  N2  +  3NaBr  +  SHp. 


91 

5.  Chlorine-water  added  in  small  quantity  to  a  solution  of 
a  bromide  liberates  bromine,  which  remains  dissolved  in  the 
water.  On  adding  a  small  quantity  of  chloroform  or  of 
carbon  disulphide  (both  of  which  are  insoluble  in  water  and 
sink  to  the  bottom  of  the  test-tube),  closing  the  mouth  of  the 
tube  with  the  thumb,  and  thoroughly  shaking  it,  the  chloro- 
form or  carbon  disulphide  extracts  the  bromine  and  collects 
at  the  bottom  of  the  tube  as  a  yellowish  or  brownish  liquid. 
The  depth  of  coloration  depends  upon  the  quantity  of  bromine 
present. 

If  an  excess  of  chlorine- water  is  used,  decolorization  of  the 
liquid  occurs,  due  to  the  formation  of  HBrOg,  bromic  acid : 

Br2  +  Cl,o  =  2BrCl,; 

BrClg  -f  3H2O  =  HBrOg  -j-  5HC1. 

HYDRIODIC  ACID,   HI. 

(Hydriodic  acid  combines  with  bases  to  form  salts  called 
iodides.) 

Kly  potassium  iodide,  may  he  employed  in  making  the  tests, 

1.  Most  of  the  iodides  (compounds  of  the  anion  I')  are 
soluble  in  Avater ;  the  others  are  soluble  in  acids,  with  the 
exception  of  argentic  iodide.  Plumbic  iodide  is  sparingly 
soluble  in  cold  water. 

2.  AgNOg,  argentic  nitrate,  precipitates  yellowish,  amor- 
phous Agl,  argentic  iodide,  insoluble  in  nitric  acid  and  in 
ammonium  hydroxide,  soluble  in  potassium  cyanide  and  in 
sodium  hyposulphite. 

3.  Pb(C2H302)2,  plumbic  acetate,  precipitates  in  solutions 
of  hydriodic  acid  and  of  iodides  yellow,  crystalline  Pbig, 
plumbic  iodide,  soluble  in  hot  water,  from  which,  on  cooling, 
it  separates  in  glistening  yellow,  six-sided  plates. 

4.  FeClg,  ferric  chloride,  added  to  a  solution  of  an  iodide 


92 

causes  a  liberation  of  iodine  in  consequence  of  the  conversion 
of  Fe*"  into  Fe": 

2FeCl3  +  2KI  =  2FeCl2  +  2KC1  +  L. 

5.  Dry  iodides,  distilled  in  a  retort  with  potassium  dichro- 
mate  and  concentrated  sulphuric  acid  (see  under  Chlorides,  4, 
page  89),  yield  violet  vapors  of  iodine  -S^^ 

6KH-  K^CrA + 7H2SO,  =  Cr2(SO,)3+ 4K2SO,+  TH^OH-  !«. 
The  iodine  contained  in  the  distillate  is  soluble  in  sodium 
hydroxide,  forming  Nal,  sodium  iodide,  and  NalOg,  sodium 
iodate,  the  distillate  at  the  same  time  becoming  colorless : 
Ifi  +  6NaOH  =  5NaI  +  NalOg  +  SHfi. 

6.  Chlorine-water  added  in  small  quantity  to  a  solution 
of  an  iodide  liberates  iodine,  which  imparts  a  yellowish  or 
brownish-yellow  color  to  the  solution.  On  adding  a  small 
quantity  of  chloroform  or  of  carbon  disulphide  to  the  liquid, 
closing  the  tube  with  the  thumb,  and  thoroughly  shaking  it, 
the  chloroform  or  carbon  disulphide  will  settle  at  the  bottom 
of  the  tube,  and  be  found  to  possess  a  pinkish-violet  color, 
due  to  the  free  iodine  extracted  from  the  aqueous  solution. 

The  addition  of  an  excess  of  chlorine  water  causes  the 
oxidation  of  the  iodine  to  iodic  acid,  with  a  consequent 
decolorization  of  the  liquid : 

I,+  C%  =  2IC1,; 

ICI5  +  3H2O  =  HIO3  +  5HC1. 
If,  instead  of  chloroform  or  carbon  disulphide,  a  drop  of 
dilute  starch  paste  is  added,  the  solution  becomes  blue,  due  to 
the  action  of  the  free  iodine  upon  the  starch.  The  test  is 
exceedingly  delicate,  and  when  considerable  iodine  is  present 
the  liquid  becomes  black  upon  the  addition  of  the  starch ; 
therefore  strong  solutions  of  iodides  should  be  diluted  before 
making  this  test. 

*  Distinction  from  chlorine  and  bromine. 


93 


HYDROCYANIC    ACID,   HCN. 


(Hydrocyanic  acid  combines  with  bases  to  form  salts  called 
cyanides.) 

KCNy  potassium  cyanide^  may  be  employed  in  making  the 
tests. 

1.  Of  the  cyanides  (compounds  of  the  anion  CN'),  those 
of  the  alkalies  and  of  the  alkaline  earths  are  soluble  in  water 
(also  mercuric  cyanide) ;  the  cyanides  of  the  heavy  metals 
are  insoluble  in  water,  although  many  of  them  are  soluble  in 
potassium  cyanide,  with  the  formation  of  double  salts,  com- 
pounds of  the  complex  anion  Ag(CN)/  ;  for  example  : 

AgCN  +  KCN  =  KAg(CN)2. 
By  the  addition  of  an  acid  to  these  solutions  the  cyanide  of 
the  heavy  metal  is  usually  but  not  invariably  reprecipitated, 
with  the  evolution  of  hydrocyanic  acid : 

KAg(CN)2  +  HNOa  =  AgCN  +  HCN  +  KNO3. 
For  methods  of  dissolving  and  fusing  cyanides,,  see  4,  page 
128. 

2.  AgNOa,  argentic  nitrate,  precipitates  in  solutions  of 
hydrocyanic  acid  and  of  cyanides  white,  curdy  AgCN,  in- 
soluble in  nitric  acid,  easily  soluble  in  ammonium  hydroxide. 
From  this  solution  it  is  reprecipitated  by  nitric  acid : 

AgCN  +  NH3  =.  NHgAgCN ; 

NHgAgCN  +  HNO3  =  AgCN  +  NH,N03. 

Argentic  cyanide  is  soluble  in  potassium  cyanide ;  therefore 

a  precipitate  appears  only  after  an  excess  of  argentic  nitrate 

has  been  added.     It  is  also  soluble  in  sodium  hyposulphite. 

On  igniting  argentic  cyanide  it  breaks  up  into  metallic  silver 

and  cyanogen  gas  (together  with  some  argentic  paracyanide)  : 

AgCN  =  Ag  +  CN. 

3.  Pb(C2H302)2,  plumbic  acetate,  produces  in  solutions  of 


94 

cyanides  a  white  precipitate  of  Pb(CN)2,  plumbic  cyanide, 
soluble  in  an  excess  of  the  reagent  and  in  nitric  acid. 

4.  If  XaOH,  sodium  hydroxide,  FeSO^,  ferrous  sulphate, 
and  FeCls,  ferric  chloride,  are  adde^l  in  small  quantities  to 
a  solution  of  hydrocyanic  acid  or  to  a  cyanide,  the  mixture 
warmed,  and  finally  acidulated  with  hydrochloric  acid,  a  blue 
precipitate  of  Fe4(Fe(CN)g)3,  ferric  ferrocyanide  (Prussian 
blue),  is  formed ;  while  the  ferrous  hydroxide  first  produced 
is  dissolved  by  the  acid.  The  ferrous  sulphate  with  the 
sodium  hydroxide  produces  Fe(OH)2,  ferrous  hydroxide : 

FeSO,  +  2XaOH  =  Fe(0H)2  +  Na^SO,, 
which,  on  being  warmed  with  the  cyanide  solution,  yields  a 
ferrocyanide ;  for  example,  with  potassium  cyanide  it  yields 
K4Fe(CX)g,  potassium  ferrocyanide : 

Fe(OH)2  -f-  6KCX  =  K,Fe(CN)6  +  2KOH, 
which  combines  with  the  iron  of  the  ferric  chloride  to  form 
blue  ferric  ferrocyanide  (Prussian  blue). 

5.  To  detect  hydrocyanic  acid  which  is  being  evolved  from 
a  liquid,  a  drop  of  yellow  ammonium  sulphide  and  of  ammo- 
nium hydroxide  is  placed  on  the  concave  side  of  a  watch- 
glass,  the  watch-glass  inverted  and  placed  as  a  cover  over  the 
vessel  in  which  the  hydrocyanic  acid  is  being  evolved,  so  that 
the  vapors  of  the  acid  coming  in  contact  with  the  ammoniacal 
liquid  can  be  absorbed.  After  some  time  the  watch-glass  is 
removed,  placed  on  a  water-bath,  and  warmed,  whereby 
NH4CNS,  ammonium  sulphocyanide,  is  produced  : 

HCN  +  (NHJ^Sg  +NH,OH  =  NH.CNS  +  {^n,\^  +  Hp, 
which  remains  as  a  dry  residue  on  the  complete  evaporation 
of  the  liquid.  This  residue  is  dissolved  in  a  little  water ;  a 
few  drops  of  hydrochloric  acid  (to  decompose  any  (NH^jgS 
remaining)  and  a  drop  of  ferric  chloride  are  added,  whereby 
a  claret-red  coloration  is  pnxluced,  due  to  the  formation  of 
Fe(CNS)3,  ferric  sulphocyanide. 


95 

6.  When  heated  in  a  reduction-tube  the  cyanides  of  the 
heavy  metals  are  decomposed ;  the  cyanides  of  the  noble 
metals  break  up  into  metal  and  cyanogen  gas ;  other  cyanides 
break  up  into  metal,  carbon,  and  nitrogen.  Argentic  and 
mercuric  cyanides,  in  which  the  cyanogen  cannot  be  detected 
by  the  ordinary  reagents,  can  be  recognized  in  this  manner. 
Mercuric  cyanide  in  aqueous  solutions,  when  ti*eated  with 
hydrogen  sulphide,  decomposes  and  forms  mercuric  sulphide 
and  hydrocyanic  acid.     HCX  and  CX  are  virulent  poisons. 

HYDROFERROCYANIC  ACID,   H^FeCCN^ 

(Hydroferrocyauic  acid  combines  with  bases  to  form  salts 
called  ferrocyanides.) 

K^Fe{CN)^,  potassium  ferroeyanide,  may  he  employed  in 
making  the  tests, 

1.  The  ferrocyanides  (compounds  of  the  complex  anion 
Fe(CN)g""),  with  the  exception  of  those  of  the  alkalies  and 
of  the  alkaline  earths,  are  mostly  insoluble  in  water.  Regard- 
ing their  solution  and  fusion,  see  page  129. 

2.  AgXOj,  argentic  nitrate,  precipitates  white  Ag^Fe(CX)j, 
argentic  ferroeyanide,  insoluble  in  nitric  acid  and  in  ammo- 
nium hydroxide,  soluble  in  potassium  cyanide. 

3.  Pb(C2H302)2,  plumbic  acetate,  in  solutions  of  ferro- 
cyanides precipitates  white  Pb2Fe(CX)g,  plumbic  ferroeyanide, 
insoluble  in  dilute  nitric  acid. 

4.  Ferrous  salts  (FeSO^,  feri-ous  sulphate)  produce  in  solu- 
tions of  ferrocyanides  (when  the  ferroeyanide  is  in  excess)  a 
white  precipitate,  which,  on  exposure  to  the  air,  rapidly 
changes  to  bluish-white  K2Fe(Fe(CX)g),  potassium  ferrous 
ferroeyanide  (Everett's  salt).  When  the  ferrous  salt  is  in 
excess,  Fe2Fe(CX)g,  ferrous  fernx'yanide,  is  produced. 

5.  Ferric   salts  (FeCla,  ferric  chloride)  precipitate  dark- 


96 

blue  Fe4(Fe(CN)g)3,  ferric  ferrocyanide  (Prussian  blue),  insol- 
uble in  acids. 

6.     CuSO^,    cupric    sulphate,    precipitates    brownish-red 
Cu2Fe(CN)g,  cupric  ferrocyanide. 


HYDROFERRICYANIC  ACID,   H3Fe(CN)6. 

(Hydroferricyanic  acid  combines  with  bases  to  form  salts 
called  ferricyanides.) 

K^Fe(CN)Q,  potassium  femcyanide,  may  he  employed  in 
making  the  tests. 

1.  Of  the  ferricyanides  (compounds  of  the  complex  anion 
Fe(CN)g'''),  those  of  the  alkalies  and  of  the  alkaline  earths 
are  soluble  in  water,  while  those  of  the  heavy  metals  are 
mostly  insoluble  in  water.  Regarding  their  solution  and 
fusion,  see  page  129. 

2.  AgNOg,  argentic  nitrate,  precipitates  from  solutions 
of  ferricyanides  reddish-brown  Ag3Fe(CN)g,  argentic  ferri- 
cyanide,  insoluble  in  nitric  acid,  soluble  in  ammonium  hy- 
droxide and  in  potassium  cyanide. 

3.  Ferrous  salts  (FeS04,  ferrous  sulphate)  precipitate 
Fe3(Fe(CN)g)2,  ferrous  ferricyanide  (TurnbulFs  blue),  insolu- 
ble in  acids.  Ferric  salts  fail  to  produce  a  precipitate,  but 
cause  a  dark  coloration  ;  possibly  soluble  Fe2(Fe(CN)6)2,  ferric 
ferricyanide,  is  produced : 

2FeCl3  +  2K3Fe(CN)g  -.  Fe,(Fe(CN)g)2  -F  6KC1. 

4.  CUSO4,  cupric  sulphate,  precipitates  greenish-yellow 
Cu3(Fe(CN)g)2,  cupric  ferricyanide. 


97 


SULPHOCYANIC    ACID,    HCNS. 

(Sulphocjanic  acid  combines  with  bases  to  form  salts 
called  sulphocyanides,  also  termed  mlphocyanates.) 

KCNSy  potassium  sulphocyanide,  may  be  employed  in  mak- 
ing the  tests. 

1.  The  sulphocyanides  (compounds  of  the  complex  anion 
CNS')  of  the  alkalies,  of  the  alkaline  earths,  and  of  the  heavy 
metals,  with  the  exception  of  mercuric  and  argentic  sulpho- 
cyanides, are  soluble  in  water. 

2.  AgNOa,  argentic  nitrate,  precipitates  in  solutions  of 
sulphocyanic  acid  and  of  sulphocyanides  white,  curdy 
AgCNS,  argentic  sulphocyanide,  insoluble  in  water  and  in 
dilute  nitric  acid,  and  which  blackens  when  exposed  to  the 
direct  rays  of  the  sun. 

3.  Pb(C2H302)2,  plumbic  acetate,  produces  a  yellowish  crys- 
talline precipitate,  Pb(CNS)2,  plumbic  sulphocyanide,  which 
forms  slowly,  and  on  being  boiled  is  converted  into  a  white 
basic  salt. 

4.  HgNOg,  mercurous  nitrate,  produces  a  white  precipitate 
of  HgCNS,  mercurous  sulphocyanide,  which  on  being  boiled 
is  resolved  into  gray,  finely  divided,  metallic  mercury  and 
Hg(CNS)2,  mercuric  sulphocyanide. 

5.  FeClg,  ferric  chloride,  produces  an  intense  claret-red 
coloration,  due  to  the  formation  of  soluble  Fe(CNS)3,  ferric 
sulphocyanide.  In  exceedingly  dilute  solutions  the  color  is 
pale  red.  HgCl2,  mercuric  chloride,  destroys  the  coloration, 
soluble  Hg(CNS)2,  mercuric  sulphocyanide,  being  formed. 


98 


SULPHYDRIC  ACID,  HjS  (HYDROGEN  SULPHIDE). 

(Sulphydric  acid  combines  with  bases  to  form  salts  called 
sulphides.) 

Na^Sf  sodium  sulphidCj  may  be  employed  in  making  the  tests, 

1.  The  sulphides  (compounds  of  the  anion  S"  and  of  the 
anion  HS'),  with  the  exception  of  those  of  the  alkalies  and  of 
the  alkaline  earths,  are  insoluble  in  water.  Most  of  them  are 
soluble  in  hydrochloric  acid  and  in  nitric  acid ;  some  are 
soluble  only  in  nitro-hydrochloric  acid.  (See  Sulphides  of 
the  Heavy  Metals,  page  128.)  They  may  be  recognized  by 
their  giving  off  hydrogen  sulphide  when  dissolved  in  hydro- 
chloric acid,  or  by  the  separation  of  sulphur  when  dissolved 
in  nitric  acid  or  in  nitro-hydrochloric  acid. 

2.  AgN03,  argentic  nitrate,  precipitates  black  AggS,  argen- 
tic sulphide,  soluble  in  nitric  acid  when  warmed. 

3.  Pb(C2H302)2,  plumbic  acetate,  precipitates  in  solutions 
of  sulphides  or  of  hydrogen  sulphide  black  PbS,  plumbic 
sulphide,  soluble  in  nitric  acid  when  warmed. 

4.  To  detect  hydrogen  sulphide  gas  a  strip  of  filter-paper 
is  moistened  with  plumbic  acetate  and  held  in  the  atmosphere 
containing  the  gas.  In  the  presence  of  hydrogen  sulphide 
the  paper  becomes  brown  or  black,  due  to  the  formation  of 
PbS,  plumbic  sulphide. 

5.  A  few  drops  of  an  alkaline  solution  of  plumbic  oxide 
(K2Pb02,  potassium  plumbite),  added  to  a  solution  contain- 
ing hydrogen  sulphide  or  a  sulphide  of  a  metal,  produces  a 
perceptible  brownish  coloration,  even  if  only  the  slightest 
trace  of  the  sulphide  be  present. 

6.  Na2NOFe(CN)5,  sodium  nitro-prusside,  solutions  are 
colored  violet  by  sulphides,  but  not  by  solutions  of  free 
hydrogen  sulphide. 

7.  Many  of  the  sulphides  of  the  metals,  when  heated  in  a 
reduction-tube,   yield   a   sublimate  of  sulphur.      Sulphides, 


99 

heated  in  a  glass  tube  open  at  both  ends  and  held  obliquely 
in  the  flame,  are  oxidized,  with  the  formation  of  SOg,  sul- 
phurous anhydride.  Ignited  with  sodium  carbonate  in  the 
reducing  flame  on  charcoal,  they  yield  sodium  sulphide,  which, 
when  placed  on  a  clean  silver  coin  and  moistened  with  water, 
produces  a  black  discoloration  of  argentic  sulphide. 


(Nitrous  acid  combines  with  bases  to  form  salts  called 
nitrites.) 

KNO2,  potassium  nitntej  may  be  employed  in  making  the 
tests. 

1.  Most  of  the  nitrites  (compounds  of  the  anion  NO2')  are 
soluble  in  water.  Treated  with  hydrochloric  or  sulphuric  acid 
they  evolve  brownish-red  fumes  of  NO2,  nitrogen  dioxide. 

2.  AgNOg,  argentic  nitrate,  precipitates  white  AgNOj, 
argentic  nitrite,  soluble  with  difficulty  in  water. 

3.  Pb(C2H302)2,  plumbic  acetate,  colors  solutions  of  nitrous 
acid  yellow. 

4.  HgS,  hydrogen  sulphide,  is  decomposed  by  nitrous  acid 
with  the  separation  of  sulphur : 

H2S  +  2HNO2  =  2NO  +  S  -h  2H2O. 

5.  FeSO^,  ferrous  sulphate,  added  to  a  solution  of  a  nitrite 
containing  a  few  drops  of  sulphuric  acid,^*^  produces  a  brown 
or  black  coloration,  due  to  the  formation  of  NO,  nitrogen 
monoxide,  which  enters  into  combination  with  the  ferrous 
sulphate : 

3FeSO,  +  H2SO,  -I-  2HNO2  =  FeSO,(NO)2  +  Fe2(SO,)3  + 

2H2O. 
Heating  the  liquid  causes  the  coloration  to  disappear. 

^  The  nitrites  of  commerce  usually  contain  free  nitrous  acid,  and  there- 
fore respond  to  the  test  without  the  addition  of  sulphuric  acid. 


100 

6.  KI,  potassium  iodide,  (or  Cdlj,  cadmium  iodide,)  starch 
paste,  and  dilute  sulphuric  acid,  added  to  a  solution  of  a 
nitrite,  immediately  produce  a  blue  coloration  in  the  liquid. 
The  nitrous  acid  liberates  iodine  from  the  hydriodic  acid  : 

2HNO2  -f  2HI  =  2NO  +  2H2O  +  I2. 
The  free  iodine  combining  with  the  starch  forms  the  blue 
compound.  (In  this  test  cadmium  iodide  or  potassium  iodide 
free  from  iodic  acid  should  be  used,  as  hydriodic  and  iodic 
acid  undergo  decomposition  when  together,  with  the  liberation 
of  iodine : 

5HI  +  HIO3  =  Ifi  +  3H2O.) 

HYPOCHLOROUS  ACID.  HCIO. 

(Hypochlorous  acid  combines  with  bases  to  form  salts 
called  hypochlorites.) 

NaClOj  sodium  hypochlorite,  may  be  employed  in  making  the 
tests, 

1.  The  hypochlorites  (compounds  of  the  anion  CIO'),  as  a 
rule,  contain  chlorides,  produced,  during  the  preparation  of  the 
hypochlorite,  by  the  action  of  the  chlorine  upon  hydroxides : 

2NaOH  +  CI2  =  NaClO  +  NaCl  +  H^O. 
On   the  addition  of  acids   they  are   decomposed,  with  the 
evolution  of  chlorine : 

NaClO  +  2HC1  =  NaCl  -f-  Cl^  +  Ilfi ; 

NaClO  +  NaCl  +  H^SO,  =  Na^SO,  +  Cl^  +  H^O. 

2.  AgNOg,  argentic  nitrate,  added  to  a  solution  of  a  hypo- 
chlorite produces  soluble  AgClO,  argentic  hypochlorite,  which 
immediately  breaks  up  into  white,  insoluble  AgCl,  argentic 
chloride,  and  soluble  AgClOg,  argentic  chlorate : 

6AgC10  =  2AgC103  +  4AgCl. 

3.  Pb(C2H302)2,  plumbic  acetate,  produces  at  first  a  white 
precipitate  of  PbCl,,  plumbic  chloride,  which  soon  becomes 


101 

yellow  and  finally  brown,  due  to  the  formation  of  PbO^, 
lead  dioxide.  (In  like  manner  MnSO^,  manganous  sulphate, 
yields  brown  MnO(OH)2,  hydrated  peroxide  of  manganese.) 


FOURTH   GROUP. 

Acids  which  are  not  precipitated  by  barium  chloride  or  by 
argentic  nitrate  :  Nitric  Acid,  Chloric  Acid. 

NITRIC  ACID,   HNO3. 

(Nitric  acid  combines  with  bases  to  form  salts  called  nitrates.) 
KNO^,  potassium  nitrate,  may  be  employed  in  making  the  tests. 

1.  The  nitrates  (compounds  of  the  anion  NO3'),  with  the 
exception  of  a  few  basic  salts,  are  soluble  in  water.  Some 
nitrates  (for  example,  Ba(N03)2,  barium  nitrate)  are  only 
sparingly  soluble  in  nitric  acid. 

2.  BaClg,  Pb(C2H302)2,  and  AgNOg  do  not  produce  pre- 
cipitates in  solutions  of  nitrates. 

3.  On  placing  a  small  crystal  of  FeSO^,  ferrous  sulphate, 
in  a  cooled  mixture  of  concentrated  sulphuric  acid  and  a 
solution  of  a  nitrate,  a  brownish-black  ring  is  formed  around 
the  crystal.  In  the  reduction  of  the  nitric  acid  NO,  nitrogen 
monoxide,  is  produced,  which  combines  with  the  ferrous 
sulphate  to  form  an  unstable  compound  : 

7FeS0,  +  3H2SO,  +  2HNO3  =  [FeS0,(N0)2]  + 
3Fe2(SO,)3  +  4H20. 
The  test  is  best  made  in  a  flat  porcelain  dish,  or  in  a  watch- 
glass  placed  on  white  paper.     Heat  destroys  the  black  ring. 

4.  KI,  potassium  iodide,  (or  Cdlj,  cadmium  iodide,)  starch 
paste,  and  dilute  sulphuric  acid,  added  to  a  solution  of  a 
nitrate,  produce  no  reaction  (distinction  from  nitrites),  but, 

9* 


102 

on  placing  a  fragment  of  zinc  in  the  liquid,  nitrous  acid  is 
evolved,  which,  acting  upon  the  potassium  iodide,  liberates 
the  iodine,  which  with  the  starch  produces  a  blue  coloration : 
HNO3  +Zn  +  H2SO,  =  HNO2  +  ZnSO,  +  Hfi  ; 
2HNO2  +  2HI  =  2NO  +  2H2O  +  I2. 
5.  Nitrates  of  the  alkalies  when  heated  in  a  reduction-tube 
are  reduced  to  nitrites,  with  the  evolution  of  oxygen  : 
KN03  =  KN02  +  0. 
The  nitrates  of  the  heavy  metals  when  heated  in  a  reduc- 
tion-tube evolve  reddish-brown  fumes  of  nitrogen  dioxide  : 

Pb(N03)2  =  PbO  +  O  +  2NO2. 
The  latter  reaction  also  takes  place  when  a  nitrate  of  an  alkali 
mixed  with  cupric  sulphate  is  heated  in  a  reduction-tube  : 
2KNO3  +  CuSO,  =  K2SO,  +CuO  +  O  +  2NO2. 
Nitrates  deflagrate  when  ignited  on  charcoal. 

CHLORIC  ACID,   HCIO3. 

(Chloric  acid  combines  with  bases  to  form  salts  called 
chlorates.) 

KClO^y  potassium  chlorate,  may  be  employed  in  making  ilu 
tests. 

1.  The  chlorates  (compounds  of  the  anion  CIO3')  are 
soluble  in  water. 

2.  BaClg,  barium  chloride,  does  not  produce  a  precipitate 
in  solutions  of  chlorates.  Pb(C2H302)2,  plumbic  acetate,  and 
AgN03,  argentic  nitrate,  do  not  produce  precipitates  if  the 
solution  o£  the  chlorate  be  free  from  chlorides. 

3.  On  warming  a  solution  of  a  chlorate  with  hydrochloric 
acid  the  liquid  becomes  greenish  yellow  in  color,  and  greenish- 
yellow  fumes  of  a  mixture  of  chlorine  and  CI2O4,  chlorine 
tetroxide  (chlorine  jxjroxide),  are  evolved  : 

KCIO3  +6HC1  :=  KCl  +  Clg  +  8H2O  ; 

2KCIO3  +  4HC1  =  2KC1  +  CI2O4  +  CI2  +  2H2O. 


103 

4.  Concentrated  sulphuric  acid  poured  over  a  vei-y  miall 
piece  of  a  chlorate  in  a  porcelain  dish  causes  a  decomposition 
of  the  chlorate,  with  the  production  of  a  perchlorate  and 
chlorine  tetroxide  (chlorine  peroxide)  : 

3KCIO3  +  2H2SO4  =  2KHSO,  +  KCIO4  +  CIA  +  H2O. 
Great  care  should  be  used  in  making  this  test,  and  only  small 
quantities  of  chlorate  should  be  employed.     Warming  should 
be  avoided,  as  explosions,  which  may  cause  personal  injury, 
are  likely  to  occur  on  the  application  of  heat. 

5.  Chlorates  heated  in  a  reduction-tube  undergo  decomposi- 
tion, and  are  converted  into  chlorides,  with  the  evolution  of 
oxygen  : 

KCIO3  =  KCl  +  O3. 
(Bromates  and  iodates  undergo  a  similar  decomposition  on 
being  heated,  forming  respectively  bromides  and  iodides,  with 
the  evolution  of  oxygen.) 

APPENDIX:    OEGANIC   ACIDS. 
Acetic  Acid,  Oxalic  Acid,  Tartaric  Acid. 


(Acetic   acid   combines   with   bases   to   form   salts   called 
acetates.) 

NaC2lI^02,  sodium  acetate,  may  be  employed  in  making  the 


1.  Most  of  the  acetates  (compounds  of  the  anion 
CH3COO',  /.  e.,  (C2H3O/)  )  are  easily  soluble  in  water. 

2.  BaClg,  barium  chloride,  and  Pb(C2H302)2,  plumbic 
acetate,  do  not  produce  precipitates  in  solutions  of  acetates. 

3.  AgN03  argentic  nitrate,  precipitates,  in  concentrated 
acetic  acid  or  in  concentrated  solutions  of  acetates,  crystalline 
AgCgHgOg,  argentic  acetate,  soluble  in  a  large  quantity  of 
water  and  in  ammonium  hydroxide. 


104 

4.  FeClg,  ferric  chloride,  added  to  a  neutral  acetate,  or  to 
acetic  acid,  which  must  afterwards  be  exactly  neutralized  with 
ammonium  hydroxide,  produces  a  reddish-brown  solution  of 
Fe(C2 1^302)3,  ferric  acetate  : 

3NaC2H302  +  FeCl3  ==  Fe(C2H302)3  +  3NaCl. 
On  warming   this  solution    a    precipitate   of  brownish-red 
Fe(OH)2C2H302,    basic   ferric   acetate,    separates,  while  the 
supernatant  liquid  becomes  colorless  : 

re(C,H30,)3  +  2H,0  =  Fe(OH),C,HA  +  2nC,Hf>,. 

5.  On  adding  sulphuric  acid  to  a  solution  of  an  acetate  and 
warming  the  liquid,  HC2H3O2,  acetic  acid,  is  liberated,  wiiich 
may  be  recognized  by  its  odor  of  vinegar. 

6.  On  adding  CgHgOH,  alcohol,  to  a  cool  solution  of  an 
acetate  containing  sulphuric  acid  and  then  w^arming  the  liquid, 
C2H5C2H3O2,  ethyl  acetate  (acetic  ether),  is  produced,  which 
may  be  recognized  by  its  characteristic  apple-like  odor  : 

C2H,OH  +  H2SO,  -  C2H,HSO,  +  H2O ; 

C2H5HSO,  +  HC2H362  =  C2H,C2H302  H-  H2SO,. 
The  alcohol  should  not  be  added  while  the  liquid  is  hot,  as 
violent  ebullition  might  occur  with  consequent  spurting  of  the 
liquid. 

7.  Acetates  on  being  ignited  are  decomposed,  without  the 
separation  of  carbon,  into  volatile  products  (for  example, 
acetone)  and  carbonates  or  oxides  of  the  metals  which  were 
in  combination  as  acetates. 

OXALIC    ACID,    H2C2O4. 

(Oxalic  acid  combines  with  bases  to  form  salts  called 
oxalates.) 

{NH^fifii,  ammonium  oxalate,  may  be  employed  in  making 
the  tests. 

1.  Of  the  oxalates  (compounds  of  the  anion  C2O/'  and 
of  the  anion  HC2O/),  those  of  the  alkalies  are  soluble  in 
water;  most  of  the  others  are  insoluble  in  water. 


105 

2.  BaClg,  barium  chloride,  precipitates  in  solutions  of 
neutral  oxalates  white  BaCgO^,  barium  oxalate,  easily  soluble 
in  hydrochloric  and  in  nitric  acid. 

3.  CaClg,  calcium  chloride,  precipitates  from  neutral  solu- 
tions of  oxalates  white  CaCgO^,  calcium  oxalate,  soluble  in 
hydrochloric  and  in  nitric  acid,  insoluble  in  acetic  acid. 

4.  Pb(C2 11302)2,  plumbic  acetate,  precipitates  white  PbC204, 
plumbic  oxalate,  soluble  in  nitric  acid. 

5.  AgNOg,  argentic  nitrate,  precipitates  white  Ag2C204^ 
argentic  oxalate,  soluble  in  nitric  acid  and  in  ammonium 
hydroxide. 

6.  Concentrated  sulphuric  acid,  on  being  warmed  with 
oxalic  acid  or  oxalates,  decomposes  them  into  water,  COg, 
carbon  dioxide,  and  CO,  carbon  monoxide  : 

H2C2O,  +  H2SO,  =  H2O  +  CO2  +  CO  +  H2SO,. 
On  pouring  the  gases  into  a  test-tube  containing  clear  solution 
of  calcium  hydroxide  (lime-water),  closing  the  tube  with  the 
thumb,  and  shaking  it,  the  production  of  a  milky  turbidity, 
due  to  the  formation  of  calcium  carbonate,  indicates  the 
presence  of  carbon  dioxide. 

7.  Oxalates  on  ignition  are  decomposed  into  carbon  mon- 
oxide and  carbonates  or  oxides  of  the  metals  which  were  in 
combination  as  oxalates.  Pure  oxalates  on  being  ignited  do 
not  become  black  in  color : 

K2C20,  =  CO  +  K2C03. 

TARTARIC    ACID,    H2C4H4O6. 

(Tartaric  acid  combines  with  bases  to  form  salts  called 
tartrates.) 

KNaCJI^Q,  potassium  sodium  tartrate,  may  be  employed 
in  making  the  tests. 

1.  The  tartrates  (compounds  of  the  anion  C^H^O/'  and 
of  the  anion  HC^H^O/)  of  the  alkalies  and  some  of  the  tar- 


106 

trates  of  the  heavy  metals  are  soluble  in  water ;  the  other 
tartrates  are  soluble  in  acids. 

2.  BaCIg,  barium  chloride,  added  in  excess  precipitates 
white  BaC4H^Og,  barium  tartrate,  soluble  in  hydrochloric  and 
in  nitric  acid. 

3.  CaClg,  calcium  chloride,  added  in  excess  precipitates 
white,  crystalline  CaC^H^Og,  calcium  tartrate,  soluble  in 
hydrochloric,  nitric,  and  acetic  acids.  The  precipitate  is  also 
soluble  in  potassium  or  sodium  hydroxides,  forming  a  clear 
liquid,  from  which,  on  boiling,  the  calcium  salt  separates  in 
gelatinous  masses.  Probably  a  salt,  CaNa2C4H20g,  is  pro- 
duced in  which  the  hydrogen  atoms  of  the  alcoholic  hydroxyl 
of  the  taiiaric  acid  have  also  been  replaced  by  a  metal : 

CaQHA  +  2NaOH  =  CaNa^C^HA  +  ^H^O. 
This  compound,  on  being  boiled  with  considerable  water,  is 
reconverted  into  the  original  calcium  tartrate : 

CaXa2C4H206  -f  2H2O  =  CaC^HPe  -f-  2NaOH. 

4.  Pb(C2H302)2;  plumbic  acetate,  precipitates  white 
PbC^H^Og,  plumbic  tartrate,  soluble  in  nitric  acid  and  in 
ammonium  hydroxide. 

5.  AgNOg,  argentic  nitrate,  precipitates  in  solutions  of 
neutral  tartrates  Ag2C4H40g,  argentic  tartrate,  soluble  in 
nitric  acid  and  in  ammonium  hydroxide.  On  boiling  the  pre- 
cipitate it  is  decomposed,  with  the  separation  of  metallic  silver. 

6.  KC2H3O2,  potassium  acetate,  in  the  presence  of  free 
acetic  acid  produces  in  concentrated  solutions  of  free  tartaric 
acid,  and  of  tartrates,  a  white  precipitate  of  KHC^H^Og,  acid 
potassium  tartrate : 

Ufijifi,  +  KC2H3O2  -  KHC^HA  -^  HC2H3O2 ; 

Na^QHA  -f  KC2H3O2  +  HC2H3O2  -  KHC.HA  + 

2NaC2H,02. 

7.  Tartrates  on  being  ignited  are  decomposed,  with  the 
production  of  an  odor  resembling  that  of  burnt  sugar,  the 
separation  of  carbon  and  the  formation  of  carbonates. 


III.    PRELIMINARY  EXAMINATION. 


(A)     PRELIMINARY  TESTS  IN  THE  DRY  WAY. 

The  special  tests  for  bases  and  acids  (testing  in  the  Wet 
Way)  are  always  preceded  by  a  short  preliminary  examina- 
tion (in  the  Dry  Way),  in  order  to  obtain  general  information 
regarding  the  nature  of  the  substance  to  be  analyzed.  It  is 
hardly  possible  to  determine  the  best  method  to  be  employed 
in  the  preparation  of  the  substance  for  analysis  without  re- 
sorting to  this  preliminary  examination.  It  should  therefore 
never  be  omitted. 

When  solutions  are  to  be  analyzed,  a  portion  is  evaporated 
to  dryness  at  a  moderate  temperature  (without  ignition),  and 
the  residue  used  for  the  preliminary  tests. 

1.    EXAMINATION    IN   THE  REDUCTION-TUBE. 

To  ascertain  the  behavior  of  the  substance  at  higher  tem- 
peratures, a  small  portion  of  it,  or  of  the  residue  obtained  by 
evaporation,  is  placed  in  a  narrow  glass  tube  closed  at  one 
end,  and  heated,  at  first  slightly,  afterwards  more  strongly, 
and  then  to  redness. 

The  occurrence  of  any  of  the  following  changes  should 
especially  be  noted : 

1.  Separation  of  Carbon:  Indicates  the  presence  of  organic 
compounds.  Simultaneously  a  generation  of  empyreumatic 
vapors  takes  place,  or,  if  nitrogen  is  present,  an  odor  of 
burnt  feathers  is  produced. 

2.  Elimination  of  Water :  Indicates  the  presence  of  water 
of   crystallization    or  of  adherent    moisture;    frequently   ^ 

107 


108 

change  of  color  occurs,  as  in  the  transformation  of  the  bhie 
hydrous  sulphate  of  copper  (CuSO^  -|-  SHgO)  into  the  an- 
hydrous salt  (CuSO^).  Intumescence  may  take  place  as  in 
the  case  of  borax  (Na^B^Oy  -j-  IOH2O),  or  decrepitation  as  in 
sodium  chloride  (in  consequence  of  the  violent  expulsion  of 
water  confined  between  the  lamellae  of  the  crystals). 

3.  Change  in  Color:  Indicates  the  presence  of  combina- 
tions of  heavy  metals.  The  change  may  be  caused  by  the 
elimination  of  water  (see  2,  page  107),  or  by  the  conversion  of 
salts  into  oxides;  for  example,  cupric  nitrate  and  cupric 
carbonate  become  black  in  color  when  heated,  due  to  their 
conversion  into  cupric  oxide  : 

Cu(N03)2  =-  CuO  +  2NO2  +  O ; 

CuC03  =  CuO  +  C02. 
Many  compounds  differ  in  color  when  hot  and  when  cold ; 
for  example,  oxide  of  zinc  is  yellow  when  hot  and  white 
when  cold. 

4.  Formation  of  a  Sublimate:  Indicates  the  presence  of 
volatile  compounds. 

(a)  White  sublimate :  Salts  of  mercury,  ammonium  salts, 
arsenious  oxide,  antimonious  oxide. — On  heating  the  sublimate 
with  dry  sodium  carbonate,  salts  of  mercury  become  red,  due 
to  the  formation  of  mercuric  oxide  (frequently  metallic  mer- 
cury is  produced  at  the  same  time)  ;  for  example  : 

HgCl2  +  Na^COg  =  HgO  +  CO^  +  2NaCl. 

Ammonium  salts  evolve  ammoniacal  gas,  which  may  be 
recognized  by  the  odor,  and  by  its  coloring  moistened  tur- 
meric-paper brown,  and  red  litmus-paper  blue  : 

WUfil  +  Na^COg  =  2NH3  +  CO2  +  H2O  4-  2NaCl. 

Arsenical  vapors  and  antimonious  oxide  are  apparently  not 
clianged  when  heated  with  sodium  carbonate.  The  arsenic 
sublimes  in  octahedral  crystals;  the  antimony  forms  an 
amorphous  sublimate,  which  sometimes  contains  crystals. 


109 

(6)  Yellow  sublimate  :  Mercuric  iodide  (becomes  red  when 
stirred),  arsenions  sulphide. 

(c)  Yellow  to  red :  Compounds  of  mercury  (formation  of 
basic  salts). 

(d)  Yellow  to  brownish  yellow :  Sulphur  (when  hot  col- 
lects in  reddish-brown  drops).  Free  sulphur,  or  sulphides 
rich  in  sulphur,— for  example,  SbgSg  =  SbgSg  +  Sg. 

(e)  Gray  to  black :  Mercury  (globules) ;  mercuric  sulphide 
(black,  red  when  rubbed) ;  iodine  (violet  vapors,  characteristic 
odor  of  iodine)  ;  arsenic  (mirror). 

It  is  to  be  remembered  that,  in  addition  to  the  sublimates 
mentioned,  quite  a  number  of  compounds  exist  which  are 
more  or  less  volatile, — for  example,  many  chlorides. 

5.  Evolution  of  Vapors: 

(a)  Colorless  vapors  should  be  tested  for  their  reaction 
with  litmus-paper.  The  acids  frequently  form  clouds  when 
escaping  from  the  tube  (in  consequence  of  their  changing  from 
the  anhydrous  to  the  hydrous  state). 

(6)  Reddish-brown  vapors :  Nitrogen  dioxide,  bromine. 
Nitrogen  dioxide,  resulting  from  the  decomposition  of  nitrates 
of  the  heavy  metals, — for  example,  Pb(N03)2  =  PbO  -(- 
2NO2  -f-  O, — does  not  color  starch-paper,  and  is  recognized 
by  its  odor.  Bromine,  also  recognizable  by  its  odor,  colors 
starch-paper  reddish  yellow. 

(c)  Violet  vapors  :  Iodine.  Characteristic  odor ;  frequently 
simultaneous  formation  of  a  black  sublimate.  Colors  starch- 
paper  blue  to  brownish  black. 

6.  Production  of  an  Odor : 

(a)  Odor  of  ammonia :  Ammonium  salts ;  compounds  of 
cyanogen  or  organic  compounds  containing  nitrogen. 

(6)  Odor  of  sulphurous  anhydride :  Resulting  from  the 
decomposition  of  sulphates. 

(c)  Odor  of  cyanogen  :    Compounds  of  cyanogen.     Cyan- 

10 


110 

ogen  gas  burns  when  ignited,  with  a  flame  pinkish  lavender 
in  color : 

CN  +  O^^CO^  +  N. 
(d)  Odor  of  garlic  :  Compounds  of  arsenic,  resulting  from 
reduction. 

7.  Evolution  of  Oxygen  (may  be  recognized  by  the  flaring 
or  re-igniting  of  a  glowing  stick  held  at  the  mouth  of  the 
tube)  :  Indicates  the  presence  of  peroxides, — for  example, 
pyrolusite,  MnOg : 

SMnOa-^MngO^  +  Og; 
of  mercuric  oxide : 

HgO  =  Hg  +  0; 
of  salts  rich  in  oxygen, — for  example : 

KC103  =  KCl  +  03. 


2.    EXAMINATION   ON   CHARCOAL. 

To  determine  the  behavior  of  substances  in  the  reducing 
flame  a  small  portion  of  the  substance,  generally  mixed  with 
dry  sodium  carbonate,  is  heated  in  a  cavity  in  the  charcoal  by 
means  of  the  reducing  flame  of  the  blowpipe/^^  The  sodium 
carbonate  is  added  in  order  to  transform  salts  and  sulphates 
into  carbonates  and  oxides  respectively, — for  example  : 

CaSO^  +  Na2C03  =  CaCOg  +  NaaSO, ; 

CuCla  -f-  Na2C03  =  CuO  +  CO^  +  2NaCl. 
The  addition  of  sodium  carbonate  is  not  necessary  in  the  case 
of  metals  that  form  metallic  globules,  oxides,  and  salts  which 
are  easily  decomposed,  as  the  alkalies  and  their  salts  are  ab- 
sorbed by  the  charcoal  (because  of  their  easy  fusibility).    The 

^  The  reducing  flame  is  obtained  by  holding  the  blowpipe  near  the  flame 
and  by  gentle  blowing  directing  it  upon  the  substance  to  be  heated.  The 
oxidizing  flame  is  obtained  by  placing  the  blowpipe  in  the  interior  of  the 
flame  and  blowing  with  force. 


Ill 

oxides  of  the  remaining  elements  may  be  recognized  by  the 
following  characteristics : 

1.  The  oxides  of  the  heavy  metals  heated  in  the  reducing 
flame  are  reduced  by  the  charcoal.  The  metals  themselves 
are  either  volatile  or  non-volatile,  may  oxidize  or  not,  and 
may  be  fusible  or  infusible ;  therefore  fused  globules  may  be 
obtained,  or  infusible  masses  and  incrustations,  the  latter 
resulting  from  the  presence  of  metals  that  volatilize  and 
oxidize.  From  plumbic  oxide,  for  example,  metallic  lead  is 
obtained : 

PbO  +  C:==Pb+CO, 

part  of  which  volatilizes,  combines  with  the  oxygen  of  the 
air,  and  is  deposited  on  the  cooler  part  of  the  charcoal  as  an 
incrustation  of  yellow  oxide  : 

Pb  +  0:=PbO. 
The  metallic  globules  differ  in  their  behavior  in  the  oxi- 
dizing flame :  some  change  into  oxides  and  others  remain 
unchanged.  The  ductility  should  also  be  ascertained ;  for 
this  purpose  the  globule  is  placed  in  a  mortar  and  struck  with 
the  pestle ;  those  which  are  ductile  are  flattened  into  plates, 
while  those  which  are  brittle  break  into  pieces  and  may  be 
pulverized  by  subsequent  rubbing. 

(a)  Fused  metallic  globules,  without  incrustation,  are 
produced  : 

Yellow  :  gold,  ductile,  not  oxidizable. 
White  :  silver,  ductile,  not  oxidizable. 
Red  :  copper, ^'^  ductile,  oxidizable. 
With  incrustation, — White  globule,  incrustation  yellow  : 
Ductile :  lead,  oxidizable. 
Brittle :  bismuth,  oxidizable. 
White  globule,  incrustation  white  : 


Generally  obtained  as  metallic  spangles. 


112 

Ductile:  tin/'^  oxidizable. 
Brittle :  antimony,  oxidizable. 

(b)  Incrustation  without  metallic  globule  : 

White  when  cold,  yellow  when  hot :  zine. 
Yellowish  red  to  brown  :  cadmium. 

(c)  Gray,  infusible  masses  : 

Iron 

Cobalt 

Nickel  ]  oxidizable. 

Manganese   J 

Platinum  :  not  oxidizable. 

(d)  Neither  globule  nor  incrustation  : 

Volatile  with  odor  of  garlic  :  arsenic. 
Volatile  without  odor  of  garlic  :  mercury. 

In  examining  metallic  globules  it  is  to  be  remembered  that 
in  the  presence  of  different  metals  alloys  may  be  formed. 

2.  White  infiLsihle  masses  remain  on  the  charcoal  if  salts 
of  the  alkaline  earths,  magnesium  or  aluminium,  are  present. 
(By  the  action  of  Na2C03,  carbonates  and  oxides  are  formed.) 
The  white  masses,  moistened  with  a  solution  of  cobaltous 
nitrate  and  strongly  heated  in  the  oxidizing  flame,  yield  as 
follows : 

Aluminium  :  blue  masses  (infusible). 

Magnesium :  pink-colored  masses. 

Barium      ^ 

Strontium    I  gray  masses. 

Calcium     J 

*  Tin  and  antimony  are  obtained  with  difficulty  in  the  form  of  globules 
when  sodium  carbonate  is  employed.  Therefore  on  the  appearance  of  a 
white  incrustation  a  second  test  is  made,  in  which,  in  addition  to  sodium 
carbonate,  potassium  cyanide  is  added  to  the  salt,  and  the  whole  heated  in 
the  reducing  flame.  (KCN  thereby  changes  into  KCNO :  for  example, 
SnOj  +  2KCN  =  Sn  +  2 KCNO.)  Compare  also  its  behavior  with  cobalt 
solution,  see  6,  page  42. 


113 

The  cobaltous  nitrate  on  being  heated  is  converted  into  co- 
baltous  oxide : 

Co(N03)2  =  CoO  +  2NO2  +  O, 
which  combines  with  akiminium  and  magnesium  compounds. 
With  barium,  strontium,  and  calcium,  mixtures  only  of  the 
oxides  are  obtained. 

Many  silicates  and  phosphates  which  are  fusible  with  diffi- 
culty, and  also  many  borates  and  arseniates,  may  form  blue 
masses  when  ignited  with  cobaltous  nitrate ;  frequently  these 
double  salts  of  cobalt  are  easily  fusible. 

Zinc  oxide,  when  ignited  with  cobaltous  nitrate,  becomes 
yellowish  green  in  color ;  antimonious  oxide,  a  dirty  green ; 
stannic  oxide,  bluish  green.  (Compounds  of  CoO  are  pro- 
duced with  the  different  oxides.) 

3.  Green  fused  masses  (consisting  of  chromic  oxide)  indi- 
cate salts  of  chromium  and  chromates. 

4.  Yellow  or  brown  fused  masses j  consisting  of  sodium  sul- 
phide, indicate  the  presence  of  compounds  containing  sulphur. 
A  portion  is  placed  on  a  silver  coin  and  moistened  with  water 
to  ascertain  whether  a  black  discoloration  of  Ag2S  is  produced. 
(See  7,  page  98.)  As  the  formation  of  sodium  sulphide  by 
the  reduction  of  salts  containing  acids  of  sulphur  requires  time, 
and,  like  all  alkali  compounds,  the  sulphide  impregnates  the 
charcoal  on  continued  heating,  these  tests  must  be  made  just 
after  the  reduction  has  taken  place  and  before  the  sodium  sul- 
phide has  been  absorbed  by  the  charcoal. 

Many  of  the  compounds  containing  sulphur, — for  example, 
the  sulphides, — when  heated  in  a  small  glass  tube  open  at 
both  ends  and  held  obliquely  in  the  flame,  yield  sulphurous 
anhydride,  which  is  easily  recognized  by  its  odor. 


10* 


114 

3.    EXAMINATION   IN   THE  FLAME. 

If  the  presence  of  alkalies  or  alkaline  earths  is  suspected, 
a  small  portion  of  the  substance,  or  of  the  residue  obtained  by 
evaporation,  is  attached  to  a  loop  of  clean  platinum  wire/^^ 
moistened  with  a  drop  of  hydrochloric  acid,  and  held  in  me 
flame  of  a  Bunsen  burner. 

The  flame  is  colored  by  the  salts  of 
Potassium  :  violet. 
Sodium :  intense  yellow. 
Barium  :  yellowish  green. 
Strontium :  crimson. 
Calcium  :  yellowish  red. 
It  must  be  remembered  that,  if  two  or  more  of  these  ele- 
ments are  present,  one  colored  flame  may  conceal  the  other. 

Salts  of  copper  and  also  boric  acid  color  the  flame  green. 
For  colored  flames  produced  by  the  rare  elements,  see  Ap- 
pendix. 

4.    EXAMINATION   BY  MEANS  OF  A   BEAD  OF  MICRO- 
COSMIC  SALT  OR  OF  BORAX. 

A  portion  of  sodium  ammonium  phosphate  (microcosmic 
salt)  is  heated  in  a  loop  of  platinum  wire  until  it  melts,  and 
forms  a  bead.  A  very  small  portion  of  the  substance  to  be 
examined  is  then  attached  to  the  clear  bead,  which  is  again 
heated  in  the  oxidizing  flame  or  in  the  oxidizing  space  of  a 
Bunsen  flame.  The  NaNH^HPO^  -f-  4H2O,  sodium  ammo- 
nium phosphate,  when  fused,  first  loses  its  water  of  crystal- 
lization and  then  changes  into  sodium  metaphosphate : 
NaNH.HPO,  =  NaPOg  +  Hp  +  NH3. 

The  sodium  metaphosphate  dissolves  most  of  the  oxides 
and  salts  (in  the  latter  a  replacement  of  the  acids  takes  place), 
and  forms  beads,  generally  characteristic  in  color : 

^  Or  the  wire  may  be  dipped  in  the  concentrated  solution  of  the  sub- 
stance to  be  examined. 


115 

CuO  +  NaPOg  =-  CuNaPO, ; 
CuSO,  +  NaPOg  =  CuNaPO^  +  SO3. 
Some  of  the  beads  change  color  in  the  reducing  flame  or  in 
the  reducing  space  of  the  Bunsen  flame  (in  consequence  of  the 
reduction  of  the  phosphates);  for  example,  the  transparent 
bluish-green  copper  bead  by  reduction  becomes  brownish-red 
and  opaque : 

CuNaPO^  +  C  =  NaPOg  +  Cu  +  CO  ; 
the  violet  manganic  oxide  bead  in  the  reducing  flame  is  con- 
verted into  the  colorless  manganous  bead  : 

Mn2(NaP04)3  +  C  =  2MnNaPO,  +  NaPOg  +  CO. 
Borax  (NaaB^O^  -|-  lOHgO)  with   oxides  and  salts  yields 
beads  similar  to  microcosmic  salt,  which  are  likewise  reducible : 
NaaB^O^  4-CuO  =  2NaB02  +  Cu(B02)2 ; 
Na^B.O^  +  CuSO,  =  2]SraB02  +  Cu(B02)2  +  SO3 ; 
2NaB02  H-  Cu(B02)2  +  C  =  Na^B.O^  +  Cu  +  CO. 
The  reduction  of  the  oxide  in  the  beads  is  often  facilitated 
by  adding  a  small  piece  of  tin  foil : 

2CuNaP04  +  Sn  =  Sn(NaPOj2  +  Cu^. 
The  following  elements^^^  produce  characteristic  colomtions 
in  the  bead  of  microcosmic  salt : 

Oxidizing  Flame.  Reducing  Flame. 

Iron  :  yellow  to  dark  red  when      Green  to  colorless, 
hot,    light   yellow   to 
colorless  when  cold. 
Nickel :  same  as  iron.  As  in  the  oxidizing  flame.^^^ 

Cobalt:  blue.  Blue. 

Manganese :  amethyst.  Colorless. 

Chromium  :  green.  Green. 

Copper :         bhie-green.  Brownish,  opaque. 


^For  beads  produced  by  the  rare  elements,  see  Appendix. 
'For  the  behavior  of  nickel  in  the  borax  bead,  see  8,  page  62. 


116 

The  remaining  oxides  yield  colorless,  transparent  or  trans- 
lucent, enamel-like  beads. 

The  behavior  of  silicic  acid  and  of  the  silicates  in  the  bead 
of  microcosmic  salt  is  characteristic.  Silicic  acid  does  not 
dissolve  in  the  bead,  but,  while  the  bead  is  in  a  state  of  fusion, 
swims  in  distinctly  outlined  masses.  The  silicates  are  decom- 
posed in  the  bead,  with  the  separation  of  undissolved  silicic 

oxide : 

NaPOs  -f  CaSiOg  =  CaNaPO,  +  SiO^. 


(B)    PRELIMINARY  TESTS  FOR  ACIDS. 

Important  conclusions  regarding  the  presence  or  absence 
of  certain  acids  may  be  drawn  from  the  behavior  of  their  salts 
with  dilute  and  concentrated  sulphuric  acid,  and  also  with 
alcohol  and  sulphuric  acid. 

1.  If  a  portion  of  the  substance  or  solution  be  placed  in  a 

test-tube  and  treated  with  dilute  sulphuric  add,  there  may  be 

evolved : 

Colored    Gases:    Greenish-yellow   chlorine   in   presence   of 
hypochlorites  (see  1,  page  100).     Moistened  potassium 
iodide  starch  paper  held  in  the  fumes  is  colored  blue. 
Reddish-brown  vapors  of  nitrogen  dioxide  from  nitrites 
(see  1,  page  99). 

Colorless  Gases  recognized  by  their  Odor:  Sulphurous  anhy- 
dride, odor  of  burning  sulphur,  from  sulphites  or  hypo- 
sulphites ;  in  the  presence  of  the  latter,  separation  of 
sulphur  also  takes  place  (see  2,  p.  77).  Detection  of 
sulphurous  anhydride  by  potassium  iodate  (see  2,  p.  75). 
Hydrocyanic  acid,  from  many  of  the  cyanides,  recognized 
by  its  odor  of  bitter  almonds,  and  also  by  the  sulpho- 
cyanide  reaction  (see  5,  page  94). 


117 

Acetic  acid,  odor  of  vinegar,  in  presence  of  acetates. 

Hydrogen  sulphide,  from  many  of  the  sulphides,  blackens 
paper  saturated  with  solution  of  plumbic  acetate  (see 
4,  page  98).  Polysulphides  evolve  hydrogen  sul- 
phide, Avith  the  separation  of  sulphur;  sulpho-acids 
may  also  separate.  (See  pages  137,  138.) 
Colorless  and  Odorless  Gas :  Carbon  dioxide  is  liberated  with 
eifervescence  from  carbonates  (to  be  confirmed  with 
calcium  hydroxide,  see  2,  page  83). 

2.  If  a  small  portion  of  the  substance  or  solution  be  treated 
with  three  or  four  times  its  volume  of  concentrated  sulphuric 
acid  and  gently  warmed,  there  may  be  evolved  : 
Colored  Gases :  Greenish-yellow  chlorine  in  presence  of  hypo- 
chlorites ;  also  when  both  chlorides  and  nitrates,  or 
chlorides  and  peroxides  are  present.     (When  chlorides 
and  nitrates  are  present,  hydrochloric  acid  and  nitric 
acid  are  simultaneously  libemted  and  react  upon  each 
other  (see  d,  page  123).      When  chlorides  and  per- 
oxides are  present,  the  liberated  hydrochloric  acid  acts 
upon  the  peroxides  (see  c,  page  123). 
Greenish-yellow  explosive  mixture  of  chlorine  and  chlo- 
rine  tetroxide,  derived   from   chlorates  (see   4,  page 
103). 
Brownish  bromine  together  with  hydrobromic  acid  de- 
rived from  bromides ;  the  gas  colors  starch  paper  red- 
dish yellow. 
Brownish-red  chromium  oxychloride  when  chlorides  and 

chromates  are  both  present  (see  4,  page  90). 
Keddish-brown  fumes  indicate  nitrites  (see  1,  page  99). 
Violet  vapors  of  iodine  from  iodides.     The  vapors  color 
moistened  starch  paper  blue. 
Colorless  Gases  recognized  by  their  Odar :  Hydrochloric  acid 


118 

vapors  from  chlorides ;  pungent  oclor,  and  render 
argentic  nitrate  solution  (on  glass  rod)  turbid  (see  2, 
page  88). 

Hydrobromic  acid  (see  above). 

Hydrofluoric  acid  from  fluorides;  of  a  strongly  acid 
odor,  etches  glass  (see  4,  page  82). 

Nitric  acid  from  nitrates,  pungent  odor.  Red  vapors 
arise  when  ferrous  sulphate  is  added. 

Sulphurous  anhydride,  odor  of  burning  sulphur,  from 
sulphites  and  hyposulphites  (see  2,  page  75,  and  2, 
page  77. — X.  B.  May  also  result  from  the  reduction 
of  the  sulphuric  acid  employed). 

Hydrogen  sulphide  from  sulphides  (see  4,  page  98). 

Acetic  acid  from  acetates,  odor  of  vinegar  (see  5,  page 
104). 
Colorless  and   Odorless   Gases:  Oxygen  (recognized  by  test 
with  glowing  wood,  see  7,  page  110)  in  presence  of  per- 
oxides, chromates,  and  permanganates  ;  for  example  : 
MnO,  -h  H2SO,  =  MnSO,  +  Ufi  +  O  ; 
2K2Cr04  +  5H2SO,  =  Cr2(S04)3  +  2K2SO,  +  SH^O 

+  O3; 
2KMn04  -f  3H2SO4  =  2MnS0,  +  K2SO,  +  SH^O 
+  0,. 

Chromates  become  green  in  color;  permanganates  are 
decolorized. 

Carbon  dioxide  from  carbonates,  effervescence  (see  2, 
page  83). 

Carbon  monoxide  (bums  with  bluish  flame)  from  organic 
substances,  usually  with  blackening  of  the  substance 
and  the  evolution  of  carbon  dioxide  and  sulphurous 
anhydride,  as  in  the  case  of  tartaric  acid.  Carbon 
monoxide  together  with  carbon  dioxide  is  evolved 
from  oxalic  acid  (without  blackening,  see  6,  page  105). 


119 

From  cyanides,  ferrocyanides,  etc.  (Cyanides,  page 
128.)  In  presence  of  the  latter  a  transitory  bluish 
coloration  appears.  In  the  case  of  tartaric  acid  the 
odor  of  burnt  sugar  is  produced. 

3.  If  a  portion  of  the  substance  be  heated  with  concentrated 
sulphuric  acid  and  alcohol^  there  is  produced,  in  the  presence 
of  acetates,  ethyl  acetate,  which  may  be  recognized  by  its 
apple-like  odor  (see  6,  page  104).  If  the  mixture  be  poured 
into  a  small  dish  and  the  alcohol  be  ignited,  the  flame  will  as- 
sume a  green  color  in  presence  of  boric  acid  (see  5,  page  81). 


IV.  SOLUTION  AND  FUSION, 


Solids  must  necessarily  be  in  solution  in  order  to  make  the 
tests  in  the  Wet  Way.  The  method  employed  in  dissolving 
the  solid  depends  upon  the  nature  of  the  substance;  with 
this  in  view,  substances  may  be  divided  into  the  following 
five  groups : 

1.  Oxides  and  salts  (in  general). 

2.  Metals  and  alloys. 

3.  Sulphides  (of  the  heavy  metals). 

4.  Cyanides  (of  the  heavy  metals). 

5.  Silicates. 

A  distinction  may  be  made  between  solution  and  fusion. 
Many  salts  cannot  be  directly  dissolved  in  water  or  acids, 
but  must  undergo  a  special  treatment  to  separate  the  acids 
from  the  bases,  as  in  the  case  of  barium  sulphate ;  the  sul- 
phuric acid  is  separated  from  the  barium  by  fusing  with 
sodium  carbonate.  By  fusion,  new  compounds  of  the  bases 
and  acids  are  obtained  which  are  soluble  in  water  or  acids. 

In  case  a  substance  is  not  entirely  soluble  in  any  one  of 
the  solvents,  it  should  be  treated  by  each  solvent  in  turn,  and 
the  solutions  analyzed  separately,  as  two  simple  analyses  are 
more  quickly  made  than  one  complex  one.  For  example,  the 
substance  is  first  boiled  with  water,  the  solution  obtained  is 
filtered  off  and  set  aside  for  examination ;  any  residue  insol- 
uble in  hot  water  is  treated  witli  nitric  acid  and  the  solution 
diluted  with  water  and  examined  separately ;  any  residue  re- 
maining after  treatment  with  nitric  acid  is  treated  with  hydro- 
chloric acid,  the  solution  diluted  with  water  and  separately 

120 


121 

examined.  By  this  procedure  a  more  distinct  iusight  into 
the  nature  of  tlie  substance  to  be  analyzed  is  obtained. 

Hard  bodies,  minerals,  etc.,  must  be  pulverized  in  a  por- 
celain or  agate  mortar  before  they  are  dissolved.  Very  hard 
minerals  are  first  crushed  in  a  steel  mortar,  and  the  coarse 
powder  thus  obtained  is  afterwards  pulverized  in  an  agate 
moiiar.  It  is  advisable  to  sift  the  powder  through  a  linen 
cloth  (previously  washed  and  dried),  remove  the  coarser 
particles  and  again  pulverize  them,  and  repeat  the  operation. 

If  the  substance  to  be  analyzed  be  an  organic  compound 
or  contain  organic  material  (as  shown  by  the  preliminary  ex- 
amination), the  organic  substance  must  be  destroyed  by  igni- 
tion and  the  residue  then  dissolved  in  water  (removing  by 
filtration  any  separated  carbon). 

1.    DISSOLVING  OXIDES  AND  SALTS. 

(a)  A  portion  of  the  substance  to  be  dissolved  is  heated 
in  a  test-tube,  with  water.  In  case  it  enters  into  solution,  a 
larger  portion  is  dissolved  and  the  liquid  employed  in  testing 
for  bases  and  acids.  If  the  substance  is  apparently  undis- 
solved, it  is  separated  by  filtration  and  the  filtrate  evapomted 
to  dryness,  to  ascertain  whether  any  of  the  original  substance 
has  entered  into  solution. 

(b)  Substances  insoluble  in  water  are  further  tested  as  to 
their  solubility  in  dilute  nitric  acid.  An  excess  of  nitric  acid 
should  be  avoided,  as  many  nitrates  soluble  in  water  are 
insoluble  in  excess  of  strong  acids. 

On  dissolving  oxides  with  nitric  acid,  nitrates  are  formed, 
and  on  dissolving  salts,  nitrates  of  the  bases  are  produced 
with  the  liberation  of  the  acids  which  were  in  combination ; 
for  example : 

Ca3(PO,),  +  6HXO3  =  3Ca(N03)2  +  2H3PO, ; 

CUCO3  -f  2HXO3  =  Cu(N03)2  +  CO2  +  H2O. 

F  11 


122 

Thus  the  presence  of  volatile  acids  becomes  evident : 

Carbonic  acid :  effervesces ;  odorless  gas ;  renders  calcium 

hydroxide  solution  turbid  (see  2,  page  83). 
Hydrocyanic  acid  :  odor  of  bitter  almonds ;  forms  am- 
monium sulphocyanide  with  ammonium  sulphide  (see 
5,  page  94). 
Hydrogen  sulphide  :  recognizable  by  its  odor  ;  blackens 
paper  saturated  with  solution  of  plumbic  acetate  (see 
4,  page  98). 
Sulphurous  acid  :  odor  of  burning  sulphur ;  colors  potas- 
sium iodate  starch  paper  blue  (see  2,  page  75). 
Under  certain  conditions  the  presence  of  iodine,  bromine, 
or  chlorine  may  become  evident  (see  2,  page  117). 

In  using  nitric  acid  as  a  solvent,  acids  which  are  soluble 
with  difficulty  may  separate :  Boric  acid,  crystalline,  easily 
soluble  in  hot  water ;  silicic  acid,  gelatinous. 

Reddish-brown  fumes  of  nitrogen  dioxide  result  from  the 
processes  of  oxidation ;  for  example,  when  mercurous  com- 
pounds are  converted  into  mercuric  compounds  : 

HgP  +  6HNO3  =  2Hg(N03)2  +  2NO2  +  3H2O. 
These  oxidations  may  interfere  with  the  results  of  the  analysis, 
especially  when  compounds  of  mercury  are  present.  After 
the  oxidation  with  nitric  acid  it  is  impossible  to  determine  the 
original  condition  of  oxidation  of  the  salt ;  for  example,  in 
the  case  of  mercury,  after  oxidation  it  cannot  be  ascertained 
whether  the  salt  was  present  originally  as  a  mercurous  or 
a  mercuric  salt.  Salts  of  mercury  which  are  insoluble  in 
water  or  in  moderately  warm  dilute  nitric  acid  are  decom- 
posed by  boiling  in  sodium  hydroxide  (compare  page  125, 
/).  Compounds  of  arsenic  should  be  dissolved,  when  pos- 
sible, in  hydrochloric  acid,  in  order  to  prevent  tlie  conver- 
sion of  arsenious  acid  into  arsenic  acid.  Plumboso-plumbic 
oxide  (red  lead)  when  treated  with  dilute  nitric  acid  is  decom- 


123 

posed  into  soluble  plumbic  nitrate  and  insoluble,  brown  lead 
dioxide : 

PbsO,  +  4HNO3  =  2Pb(N03)2  +  PbO^  +  2H2O. 
The  latter  is  converted  into  plumbic  chloride  by  concentrated 
hydrochloric  acid. 

(c)  Those  substances  which  are  insoluble  in  dilute  nitric 
acid  must  be  treated  with  concentrated  hydrochloric  acid.     If 
in  dissolving  the  substance  in  hydrochloric  acid  chlorine  gas 
is  evolved,  peroxides  and  similar  compounds,  such  as  manga- 
nese dioxide,  chromic  acid,  or  permanganic  acid,  are  present : 
MnO,  +  4HC1  =  MnCl^  +  Cl^  +  2H2O ; 
2Cr03  +  12HC1  =2CrCl3+  C\,  +6Rfi  ; 
Mn^O^  -h  14HC1  =  2MnCl2  +  Cl^o  +  TH^O. 
Lead  dioxide  is  converted  into  plumbic  chloride,  which  crys- 
tallizes as  the  solution  cools ;  plumbic  chloride  is  best  de- 
composed with  sodium  carbonate  (page  123,  e). 

{d)  Many  compounds  insoluble  in  nitric  acid  or  in  hydro- 
chloric acid  are  soluble  in  nitro-hydrochloric  acid  (aqua  regia). 
In  dissolving  with    nitro-hydrochloric   acid    chlorine^*^  is 
liberated,  which  is  the  active  agent  in  effecting  solution  : 

3HC1 H-  HNO3  =-.  CI3  +  NO  +  2H2O. 
Nitro-hydrochloric  acid  is  prepared  by  mixing  about  three 
volumes  of  concentrated  hydrochloric  acid  with  one  volume 
of  concentrateii  nitric  acid ;  the  reaction  takes  place  upon  the 
application  of  heat.  When  nitro-hydrochloric  acid  is  em- 
ployed as  a  solvent,  oxidation  necessarily  occurs  if  the  sub- 
stance is  capable  of  being  oxidized,  as,  for  example,  with 
compounds  of  mercury. 

(e)  Many  compounds  that  are  insoluble  in  water  and  in 
acids  are  decomposed  by  boiling  or  fusing  with  carbonates  of 
the  alkalies, — that  is,  they  are  convei*ted  into  soluble  com- 

*  Besides  (NOCl)  nitrosyl  chloride  and  (NOjCl)  nitroxyl  chloride. 


124 

pounds.  Among  them  are  plumbic  sulphate,  the  sulphates 
of  the  alkaline  earths,  plumbic  chloride,  plumbic  iodide, 
stannic  oxide,  etc. 

Of  the  sulphates,  plumbic  sulphate  and  calcium  sulphate 
are  easily  decomposed  by  boiling  in  a  solution  of  sodium 
carbonate.  Precipitated  strontium  sulphate  is  also  decom- 
posed in  the  same  manner,  although  with  more  difficulty. 
Precipitated  barium  sulphate  is  only  partly  decomposed  by 
boiling  with  sodium  carbonate  solution.  These  sulphates  (as 
well  as  minerals)  are  readily  decomposed  by  being  fused  with 
from  four  to  six  parts  of  sodium  potassium  carbonate.^^^  In 
these  decompositions  the  acid  of  the  substance  fused  unites 
with  the  alkalies,  and  the  base  is  converted  into  a  carbonate ; 
for  example,  with  BaSO^  and  NaKC03  the  compounds 
NaKS04,  soluble  in  water,  and  BaCOg,  soluble  in  acids,  are 
formed : 

NaKCOs  +  BaSO,  =  NaKSO^  +  BaCOg. 

The  fused  mass  is  completely  extracted  with  hot  water  and 
the  insoluble  residue  (after  separation  by  filtering)  is  dissolved 
in  hydrochloric  acid  or  nitric  acid.  The  aqueous  solution  is 
to  be  examined  for  the  acid,  and  the  acid  solution  for  the 


Plumbic  chloride  and  plumbic  iodide,  etc.,  when  boiled 
with  a  solution  of  sodium  carbonate,  are  decomposed  respec- 
tively into  chloride  and  iodide  of  sodium  and  plumbic 
carbonate : 


^  The  double  salt  NaKCOg  fuses  more  easily  than  the  sodium  or  potas- 
sium salt  alone.  The  fusion  is  best  made  in  a  platinum  crucible,  as 
porcelain  is  attacked  by  the  alkali  carbonates.  The  following  substances 
should  never  be  fused  in  a  platinum  crucible  :  potassium  and  sodium 
hydroxide,  nitrates  and  cyanides  of  the  alkalies,  metals  and  metallic 
sulphides,  or  any  substance  from  which  a  metal  may  be  obtained  by 
reduction  or  substances  from  which  chlorine  may  be  evolved. 


125 

PbCla  +  Na^COj  =  2NaCl  +  PbCOg. 
(Plumbic  carbonate  is  slightly  soluble  in  sodium  carbonate.) 

Stannic  oxide  (cassiterite)  when  fused  with  a  carbonate  of 
an  alkali  is  converted  into  a  stannate  of  the  alkali,  which  is 
soluble  in  water  and  in  hydrochloric  acid : 
SnO.  +  K2CO3  =  K^SnOg  +  CO, ; 
K2Sn03  +  6HC1  =  SnCl,  +  2KC1  +  3H,0. 
Fusion  is  continued  until  carbon  dioxide  ceases  to  be  evolved. 
As  stannic  oxide  is  acted  upon  only  wdth  great  difficulty  by 
sodium  carbonate,  it  is  best  fused  in  a  silver  crucible  wdth 
sodium  or  potassium  hydroxide,^^^  and  the  fused  mass  treated 
with  water  and  hydrochloric  acid,  as  mentioned  above. 

(/)  Many  substances  are  unacted  upon  by  the  carbonates  of 
the  alkalies,  but  are  readily  decomposed  on  being  boiled  with 
sodium  or  potassium  hydroxide ;  for  example,  mercury  and 
silver  compounds.  An  oxide  of  the  metal  is  formed,  while 
the  acid  remains  in  solution  in  combination  with  the  alkali. 
The  oxide  after  being  washed  is  dissolved  in  nitric  acid. 
2HgCl  4-  2NaOH  =  Hg^O  +  2XaCl  +  H^O. 

In  dissolving  compounds  of  mercury  cold  dilute  nitric  acid 
should  be  used,  in  order  to  avoid  the  oxidation  of  mercurous 
salts  to  mercuric  salts.  (Mercuric  iodide,  which  partly  redis- 
solves  in  a  carbonate  of  an  alkali, — i.e.,  in  the  iodide  of  the 
alkali  which  is  formed, — should  be  dissolved  in  nitro-hydro- 
chloric  acid.) 

{g)  Compounds  of  fluorine  (for  example,  fluor  spar)  are 
decomposed  by  being  gently  heated  with  concentrated  sul- 
phuric acid  in  a  platinum  crucible  : 

1  Or  it  may  be  fused  in  a  porcelain  crucible  with  three  parts  of  sodium 
carbonate  and  three  parts  of  sulphur  to  one  part  of  the  substance,  and  the 
fused  mass,  after  cooling,  extracted  with  water.  The  yellow  solution  con- 
tains the  tin  as  sulphostannate,  NajSnSg ;  the  insoluble  residue,  containing 
sulphides,  is  to  be  examined  further  according  to  3,  page  128. 

11* 


126 

CaF^  +  H2SO,  =  CaSO,  +  2HF. 
The  hydrofluoric  acid  is  recognized  by  its  etching  glass  (see 
4,  page  82) ;  the  residue  in  the  crucible,  consisting  of  sul- 
phates, is   dissolved   in   hydrochloric  acid  or,  if  necessary, 
fused  with  sodium  carbonate. 

Silicates  containing  fluorine,  if  treated  in  this  manner, 
yield  silicon  fluoride,  according  to  the  reaction  : 

2CaF2  +  Si02  +  2H2SO,  =  SiF,  +  2CaSO,  +  2H2O. 
If  the  evolved  gas  be  conducted  through  a  glass  tube  moist- 
ened with  water,  silicic  acid  together  with  hydrofluosilicic  acid 
is  produced : 

SSiF^  +  3H2O  ^  2H2SiF6  +  H2Si03. 
The  silicic  acid  will  appear,  either  directly  or  on  drying  the 
tube,  in  the  form  of  a  white  coating  (see  5,  page  82). 

(h)  Chromic  oxide,  chromite,  aluminium  oxide,  and  ferric 
oxide  are  best  fused  by  mixing  them  with  ten  parts  of  acid 
potassium  sulphate.  If  the  heat  applied  is  not  too  great, 
neutral  sulphates  (together  with  basic  salts)  are  formed  : 
AlA  +  6KHSO,  =  A\,{SO,),  +  SK^SO^  +  SH^O, 
which,  on  cooling,  may  be  dissolved  by  water  or  hydrochloric 
acid. 

Chromite  is  best  fused  with  acid  potassium  sulphate,  and 
the  fused  mass  obtained  again  fus^d  with  potassium  chlorate 
and  potassium  carbonate,  to  convert  the  chromic  oxide  into 
chromic  acid : 

Cr2(S04)3  +  3K2CO3  =  Crfi^  +  3K2SO,  +  3CO2 ; 

Cr203  +  2K2CO3  +  KCIO3  =  2K2CrO,  +  KCl  +  2CO2. 
The  fused  mass  yields  potassium  chromate  when  extracted 
with  water ;  the  residue,  consisting  of  ferric  oxide  (with  some 
chromic  oxide)  is  dissolved  in  hydrochloric  acid.    ^ 

(i)  Carbon  (charcoal,  graphite)  and  sulphur  are  recognized 
by  their  appearance  and  their  behavior  when  heated. 


127 

2.    THE  DISSOLVING  OF  METALS  AND  ALLOYS. 

Metals  and  alloys  are  cut  into  small  preces,  or  filed,  and 
the  cuttings  or  filings  are  heated  with  strong  nitric  acid  until 
brownish  fumes  cease  to  be  produced  on  further  addition  of 
acid.  The  excess  of  acid  is  evaporated  on  a  water-bath  and 
the  residue  is  heated  with  water  and  a  small  quantity  of  nitric 
acid.  Most  of  the  metals  enter  into  solution  as  nitrates,  gold 
and  platinum  remain  unchanged,  tin  is  converted  into  white 
meta-stannic  acid,  and  antimony  into  its  oxides. 

A.  If  complete  solution  has  occurred  the  solutica  is  diluted  with  water 
and  treated  with  hydrochloric  acid ;  should  precipitation  occur,  the  pre- 
cipitate is  collected  on  a  filter  and  examined  according  to  Separation  of 
First  Group  (page  146).  The  filtrate,  or  the  solution  in  which  hydro- 
chloric acid  failed  to  produce  a  precipitate,  is  evaporated  to  dryness  on  a 
water-bath,  the  residue  is  moistened  with  hydrochloric  acid,  and  again 
evaporated  to  dryness.  The  residue  is  then  moistened  with  hydrochloric 
acid  and  dissolved  in  water,  and  the  solution  examined  according  to 
Second  Group,  p.  148,  and  the  succeeding  group  reagents.  The  yellow 
ammonium  sulphide  treatment  of  the  hydrogen  sulphide  precipitate  in 
the  Second  Group  may  be  omitted. 

B.  If  a  white  residue  remain  after  treatment  with  water  and  nitric  acid, 
the  liquid  is  diluted  with  water,  filtered,  and  the  filtrate  treated  according 
to  A  above.  The  white  residue,  which  may  contain  tin,  antimony,  and 
arsenic  (the  latter  in  the  presence  of  tin,  as  arseniate  of  tin),  is  washed  with 
hot  water  until  free  from  acid,  and  is  then  heated  with  an  excess  of  yellow 
ammonium  sulphide,  whereby  tin,  antimony,  and  arsenic  are  dissolved 
as  sulpho-salts,(i)  and  the  solution  is  examined  according  to  I  ,  p.  152. 

If  after  treating  the  white  residue  with  yellow  ammonium  sulphide  an 
insoluble  residue  remain,  it  is  heated  with  strong  nitric  acid,  and  if  it  fail 
to  dissolve  it  is  treated  with  nitro-hydrochloric  acid,  which  dissolves  gold 
and  platinum  as  chlorides. (2)  The  solution  is  evaporated  to  dryness,  the 
residue  dissolved  in  water,  and  treated  according  to  Second  Group,  p.  148. 

I  Sn(0H)4  +  3(NH4)2S  =  (NH4)2SnS3  +  4NH3  +  4H2O; 

SbgOa  +  6(NH4)2S  +  83  =  2(NH4)3SbS4  +  6NH3  +  SHjO; 

SbgOi  +  7(NH4)2S  +  S  =  2(NH4)3SbS4  +  8NH3  +  mjO; 

SbaOfi  +  8(NH4)2S  =  2(NH4)3SbS4  +  IONH3  +  5HjO; 

AsgOe  +  8(NH4)2S  =  2(NH4)3AsS4  +  IONH3  -f  SHjO. 
«  Au  +  3HC1  +  HNO3  =  AUCI3  +  NO  +  2H2O  ; 

3Pt  +  12HC1  +  4HN08  -=  SPtCU  +  -iNO  +  SHsO. 


128 


3.  SULPHIDES  OF  THE  HEAVY  METALS. 

The  sulphides  of  the  heavy  metals  generally  possess  a 
metallic  lustre ;  like  the  metals  they  are  treated  with  concen- 
trated nitric  acid,  whereby  most  of  them  are  dissolved  as 
nitrates : 

CuS  +  4HNO3  =  Cu(N03)2  +  S  +  2NO2  +  2H2O. 
The  procedure  is  as  given  under  2,  page  127.  The  sulphur 
which  separates  first  is  oxidized  by  the  nitric  acid  to  sulphuric 
acid.  The  insoluble  residue,  in  addition  to  the  oxides  of  tin, 
antimony,  and  arsenic,  may  contain  PbSO^,  BiONOg  (formed 
on  treating  the  nitrate  with  water),  and  HgS.  This  residue 
is  treated  with  yellow  ammonium  sulphide,  which  dissolves 
tin,  antimony,  and  arsenic.  Any  residue  remaining  is  filtered 
off  and  treated  with  nitric  acid  to  dissolve  the  lead  and  bis- 
muth (which  at  this  stage  may  be  found  again  as  sulphides), 
and  any  residue  of  mercuric  sulphide  is  collected  on  a  filter 
and  dissolved  by  nitro-hydrochloric  acid  : 
3HgS  +  6HC1  +  2HNb3  =:  SHgCl^  +  2NO  +  4H2O  +  S3. 
Finally,  silicious  gangue,  barite,  etc.,  may  remain,  which 
should  be  examined  according  to  5  (page  130)  and  1  (page 
121)  respectively. 

The  sulphides  are  easily  recognized  by  their  appearance, 
and  also  by  their  behavior  in  the  preliminary  examination. 

4.    CYANIDES. 

The  simple  cyanides,  which  are  insoluble  in  water,  may  be 
decomposed  into  chlorides  and  hydrocyanic  acid,  by  boiling 
with  concentrated  hydrochloric  acid. 

Argentic  cyanide  and  mercuric  cyanide,  in  which  the  cyan- 
ogen cannot  be  detected  by  the  ordinary  methods,  may  be 
readily  recognized  by  their  ]>ehavior  when  heated,  as  they 
separate  into  metal  and  cyanogen.     If  the  cyanide  is  heated 


129 

in  a  narrow  glass  tube,  the  escaping  cyanogen  may  be  ignited, 
burning  with  a  pinkish-lavender  flame.  The  gas  is  also  rec- 
ognizable by  its  odor  of  bitter  almonds.  Mercuric  cyanide 
may  be  decomposed  by  dissolving  in  water  and  passing  hy- 
drogen sulphide  through  the  solution ;  mercuric  sulphide  is 
precipitated  and  hydrocyanic  acid  enters  into  solution. 

The  insoluble  compounds  of  ferrocyanogen  and  ferricy- 
anogen  are  decomposed  by  boiling  with  sodium  carbonate  or 
sodium  hydroxide ;  sodium  ferrocyanide  and  ferricyanide 
respectively  are  formed,  together  with  an  insoluble  carbonate 
or  an  oxide  of  the  metal : 

Pb2Fe(CN)6  H-  2Na2C03  =  Na,Fe(CN)6  +  2PbC03 ; 

Cu2Fe(CN)6  +  4NaOH  =  ]S'a4Fe(CN)6  +  2CuO  +  2H2O. 
The  aqueous  solution  is  filtered  and  the  filtrate  tested  for  the 
acid,  while  the  carbonates  or  oxides  are  dissolved  in  dilute 
nitric  acid.  If  sodium  hydroxide  is  employed  as  the  decom- 
posing agent,  lead,  zinc,  and  aluminium,  and  also  arsenic, 
antimony,  and  tin,  may  enter  into  solution.  In  such  cases  a 
portion  of  the  alkaline  solution  is  tested  for  lead,  zinc,  and 
aluminium  by  saturating  the  solution  with  hydrogen  sul- 
phide, thereby  precipitating  the  first  two  metals  as  sulphides 
and  the  last  as  hydroxide.  The  filtrate  from  any  precipitate 
which  may  have  been  produced,  or  the  clear  solution  if  no 
precipitate  was  produced  by  hydrogen  sulphide,  is  acidulated 
with  hydrochloric  acid  to  precipitate  arsenic,  antimony,  and 
tin  as  sulphides. 

If  sodium  hydroxide  is  used  in  decomposing  the  ferri- 
cyanide, sodium  ferricyanide  is  formed,  providing  the  metallic 
oxide  produced  in  the  operation  is  not  further  oxidizable  : 
Cu3(Fe(CN)6)2  +  6NaOH  =  2Na3Fe(CN)6  +  3CuO  +  SHp. 
If,  however,  the  separated  oxide  is  capable  of  further  oxida- 
tion, this  oxidation  takes  place,  accompanied  by  the  reduction 
of  the  sodium  ferricyanide  to  sodium  ferrocyanide : 


130 

Fe,{Fe(Cl^\\  +  8NaOH  =  2Na3Fe(CN)e  +  3Fe(OH)2  + 

2NaOH ; 

2Na3Fe(CN)6  +  3Fe(OH)2  +  2NaOH  =  2Na,Fe(CN)g  + 

2Fe(OH)3+Fe(OH),. 

Consequently,  in  such  cases  to  detect  the  acid  the  substance 

is  fused,  whenever  possible,  with  sodium  carbonate. 

To  detect  alkalies  in  ferrocyanogen  and  ferricyanogen  com- 
pounds, the  latter  are  decomposed  into  sulphates,  carbon 
monoxide,  and  ammonium  sulphate,  by  being  heated  with 
concentrated  sulphuric  acid  : 

CuK2Fe(CN)6  +  GH^SO,  +  GH^O  =  FeSO,  +  CuSO,  + 
K2SO,  +  6CO  +  3(N.H,)2SO,. 

5.    SILICATES. 

Before  silicates  can  be  analyzed  they  must  be  finely  pul- 
verized (page  121). 

(a)  Silicates  soluble  in  water  or  silicates  that  may  be  decom- 
posed by  acids  are  best  decomposed  by  being  boiled  with  con- 
centrated hydrochloric  acid ;  by  this  procedure  silicic  acid  and 
chlorides  of  the  respective  metals  are  formed  ;  for  example  : 

K2Si03  +  2HC1  =  H^SiOg  +  2KC1. 
Boiling  is  continued  until  complete  decomposition  has  taken 
place,  and  no  gritty  particles  are  detected  on  stirring  with  a 
glass  rod.  The  solution  is  then  evaporated  to  the  dryness 
of  dust  on  a  water-bath  (see  1,  page  84),  to  convert  the  solu- 
ble silicic  acid  into  insoluble  amorphous  silicic  acid.  The 
dry  residue  is  then  moistened  with  a  little  concentrated  hydro- 
chloric acid,  to  convert  any  basic  chlorides  (of  Fe,  Al,  Mg, 
etc.)  into  neutral  chlorides,  thereby  rendering  them  soluble ; 
finally  the  chlorides  of  the  bases  are  extracted  with  water  and 
dilute  hydrochloric  acid. 

(b)  Silicates  that  are  not  decomposed  by  acids  must  either 
be  fused  with  a  carbonate  of  an  alkali   or  decomposed  by 


131 

hydrofluoric  acid.  To  determine  which  method  should  be 
employed,  the  silicate  is  tested  for  the  presence  of  an  alkali. 
For  this  purpose  a  small  portion  of  the  powdered  silicate, 
moistened  with  hydrochloric  acid,  is  placed  on  a  platinum  wire 
and  held  in  the  non-luminous  flame  of  a  Bunsen  burner,  to 
observe  whether  a  color  is  imparted  to  the  flame  (sodium, 
yellow ;  potassium,  violet).  If  alkalies  are  absent  the  method 
of  decomposition  by  means  of  sodium  carbonate  is  to  be  em- 
ployed ;  whereas  if  alkalies  are  present,  in  order  to  test  for 
them,  the  silicate  must  be  decomposed  with  hydrofluoric  acid. 

(c)  In  case  the  fusion  is  to  be  made  with  sodium  carbonate 
(preferably  with  sodium  potassium  carbonate),  one  part  of  the 
finely  pulverized  substance  is  thoroughly  mixed  with  six  parts 
of  sodium  potassium  carbonate,  placed  in  a  platinum  cruci- 
ble, and  the  mixture  fused  by  means  of  the  blast-lamp.  The 
silicate  is  decomposed  by  the  carbonate  of  an  alkali,  with  the 
production  of  a  silicate  of  the  alkali  (or  at  least  silicates  that 
are  decomposed  by  acids)  and  a  carbonate  of  the  metal  : 

CaSiOs  -I-  XaKCOg  -■  NaKSiOg  +  CaCOg ; 

CaSi  A  +  2NaKC03  -=  2NaKSi03  +  CslCO,  -f  CO^. 
On  disintegrating  the  fused  mass  with  hydrochloric  acid,  ac- 
cording to  a,  page  130,  silicic  acid  remains  insoluble,  and  the 
chlorides  of  the  metals  together  with  sodium  chloride  and 
potassium  chloride  enter  into  solution. 

(d)  In  using  hydrofluoric  acid  as  a  solvent  the  finely  pulver- 
ized substance  is  placed  in  a  platinum  crucible,  and  treated  witli 
the  pure  acid^'^  until  a  thin  paste  is  formed.  The  mixture  is 
stirred  with  a  platinum  wire  (not  with  a  glass  rod)  and  digested, 
at  a  very  gentle  heat,  until  the  substance  is  completely  dissolved. 
By  this  treatment  the  silicates  are  converted  into  fluosilicates : 

^  The  hydrofluoric  acid  must  he  free  from  alkalies,  and,  when  possible, 
freshly  distilled  in  a  platinum  still. 


132 

CaSiOs  +  6HF  =  CaSiFg  +  SHp ; 
CaSiA  +  12HF  =  CaSiFfi  +  H2SiF6  +  5H2O. 
When  completely  dissolved  concentrated  sulphuric  acid  is 
added  and  heat  applied,  gently  at  first,  but  afterwards  more 
strongly,  to  drive  off  the  excess  of  acid.  The  sulphuric  acid 
converts  the  fluosilicates  into  sulphates,  while  hydrofluosilicic 
acid  is  evolved : 

CaSiFfi  +  H2SO4  =  H^SiFfi  +  CaSO,. 
The  residue  of  sulphates  is  dissolved  in  water  and  a  little 
hydrochloric  acid. 

When  this  method  is  employed  to  decompose  silicates  con- 
taining barium,  strontium,  or  calcium,  it  is  necessary — espe- 
cially with  barium  and  strontium, — to  afterwards  fuse  the 
residue  containing  the  barium,  strontium,  or  calcium  sulphate 
with  a  carbonate  of  an  alkali  (page  123,  e). 

In  mineral  analyses  it  is  often  of  interest  to  ascertain 
whether  the  minerals  contain,  in  addition  to  the  silicates  not 
decomposable  by  acids,  others  that  may  be  decomposed,  thus 
making  separation  possible  With  this  in  view,  after  having 
mechanically  separated  the  gangue  and  any  other  impurities 
from  the  mineral  proper,  it  is  finely  pulverized,  treated  with 
hydrochloric  acid,  the  solution  evaporated  to  dryness  as  above 
described  (page  130,  a),  and  the  chlorides  resulting  from  the 
decomposed  silicates  dissolved  in  water.  The  insoluble  residue, 
which  may  contain  silicic  acid  and  undecomposed  silicates,  is 
boiled  with  sodium  carbonate,  which  dissolves  the  silicic  acid 
derived  from  the  decomposed  silicate.  After  acidulating  the 
sodium  carbonate  solution  with  hydrochloric  acid,  evaporating 
to  dryness,  and  extracting  with  hot  water,  the  silicic  acid  re- 
mains as  a  light,  white  powder.  If  a  residue  remain  after 
boiling  a  second  time  with  sodium  carbonate,  it  is  to  be  con- 
sidered an  undecomposable  silicate,  which  is  to  be  further 
tested  according  to  b,  c,  and  r/,  pages  130  and  131. 


V.  DETECTION  OF  BASES  IN  THE  WET  WAY. 


If  the  substance  to  be  analyzed  is  a  solid  it  is  to  be  dis- 
solved, as  before  described  (page  121). 

To  test  for  bases  in  organic  substances  the  latter  should  be 
incinerated  and  the  bases  extracted  from  the  ash  by  water  or 
acids.  Organic  acids,  etc.,  interfere  with  a  number  of  the 
reactions  used  in  the  detection  of  bases. 

The  reaction  of  solutions  to  be  examined  should  be  tested 
with  litmus  and  turmeric  paper  to  ascertain  whether  they  are 
neutral,  acid,  or  alkaline.  A  number  of  substances  may  be 
present  in  acid  solutions,  which,  in  neutral  solutions,  may  be 
disregarded  ;  for  example,  in  the  Third  Group,  acid  solutions 
must  be  tested  for  phosphates  and  oxalates,  whereas  if  the  so- 
lutions are  neutral  the  tests  for  these  acids  need  not  be  made. 

Regarding  combinations  that  may  arise  during  the  exam- 
ination of  alkaline  solutions  see  h,  page  138. 


PRECIPITATION  OF  THE  DIFFERENT  GROUPS. 

To  separate  the  bases  into  groups  the  following  group 
reagents  are  employed  in  turn  : 

1.  Hydrochloric  acid. 

2.  Hydrogen  sulphide  (in  presence  of  HCl). 

3.  Ammonium  hydroxide  (in  presence  of  NH^Cl). 

4.  Ammonium  sulphide  (in  presence  of  NH^Cl). 

5.  Ammonium  carbonate. 

By  each  of  these  reagents  a  series  of  bases  called  a  group 
is  precipitated.  Bases  that  are  not  precipitated  by  group 
reagents  are  classed  as  a  sixth  group.  (See  Sixth  Group,  page 
145.)      The  rare  elements  are  not  considered  in  this  plan. 


12  133 


134 


TABLE  I.— GROUP  PRECIPITATIONS. 


Gboup  I. 

Metals  precipitated  by  Hy- 
drochloric Acid. 


as  white,  curdy 
AgCl,  argentic  chloride. 

Mercurous  saMs, 

as  white,  pulverulent 
HgCl,   mercurous    chlo- 
ride. 

Lead, 
as  white 
PbCla,  plumbic  chloride. 


Group  II. 
Metals  precipitated  in  Acid 
Solution      by     Hydrogen 
Sulphide. 


Lead, 
as  black 
PbS,  plumbic  sulphide. 

Mercwic  salts, 

as  black 
HgS,  mercuric  sulphide. 

Copper, 
as  black 
CuS,  cupric  sulphide. 

Bismuth, 

as  brownish-black 
BigSa,     bismuthous     sul- 
phide. 

Stannous  salts, 

as  brownish-black 
SnS,  stannous  sulphide. 

Cadmium, 

as  yellow 

CdS,  cadmium  sulphide. 

Arsenic, 

as  yellow 

AS2S3,  arssnious  sulphide 
(mixed  with  sulphur 
if  precipitated  from 
arsenic  acid  solutions). 

Stannic  salts, 

as  yellow 
SnSa,  stannic  sulphide. 

Antimonious  salts, 

as  orange-red 
Sb2S3,    antimonious    sul- 
phide. 

Antimonic  salts, 

as  orange-red 

Sb2S5,  antimonic  sulphide 

(together   with    81)283 

and  sulphur). 

Gold, 
as  black 
AU2S3,  auric  sulphide. 

Platinum, 

as  brownish-black 
PtSg,  platinic  sulphide. 


Group  III. 
Metala  precipitated  by  Am- 
monium     Hydroxide     in 
presence    of     Ammonium 
Chloride. 


Iron, 

as  reddish- brown 
Fe(0H)3,  ferric  hydroxide. 

Chromium, 

as  bluish-  or  grayish -green 
Cr(0H)8,  chromic  hydrox- 
ide. 


Aluminium, 

as  white,  gelatinous 
Al(0H')8,   aluminium    hy- 
droxide. 

In  presence  of  phosphoric 
acid  iron  and  alumin- 
ium respectively  are  pre- 
cipitated as  phosphates, 
— thus : 

Iron, 

as  white 

FeP04,  ferric  phosphate. 

Aluminium, 

as  white 

AIPO4,  aluminium 
phosphate. 

In  presence  of  phosphoric 
acid  or  oxalic  acid  cal- 
cium, strontium,  and 
barium  are  precipitated 
as  phosphates  or  oxa- 
lates, as  white 
Ca3(P04)2,  SrCaOi,  etc. 

Magnesium  in  the  pres- 
ence of  phosphoric  acid 
is  precipitated  in  this 
group 

as  white 

MgNH4P04,    ammonium 
magnesium  phosphate. 

In  presence  of  iron,  man- 
ganese may  be  precipi- 
tated 
as  white 

Mn(0H)2,  manganous  hy- 
droxide, 
changing  to  brown 
Mn(0H)3,    manganic    hy- 
droxide. 


135 


TABLE   I.— GROUP   PRECIPITATIONS.— Om^mwecf. 


Group  IV, 
Metals       precipitated       by 
Ammonium  Sulphide    in 
presence    of    Ammonium 
Chloride. 


Manganese, 
as  light-salmon-colored 
MnS,     manganous      sul- 
phide. 

Zinc, 
as  white 

ZnS,  zinc  sulphide. 

Nickel, 
as  black 
NiS,  nickelous  sulphide. 

Cobalt, 
as  black 
CoS,  cobaltous  sulphide. 


Group  V. 

Metals  precipitated  by  Am- 
monium Carbonate. 


Barium, 

as  white 

BaCOs,  barium  carbonate. 

Strontium, 
as  white 

SrCOs,  strontium  carbon- 
ate. 

Calcium, 
as  white 

CaCOs,   calcium   carbon- 
ate. 


Group  VI. 

For  which  there  is  no  Spe- 
cial Group  Reagent. 


Magnesium. 
Potassium. 

Sodium. 

Lithium. 
Ammonium, 


136 

If  on  the  addition  of  the  reagent  a  precipitate  is  formed, 
it  is  filtered  off  and  carefully  washed.  The  filtrate  should  be 
tested  to  ascertain  whether  the  precipitation  was  complete, — 
that  is,  whether  no  precipitation  takes  place  on  further  addi- 
tion of  the  reagent.  The  precipitate  must  be  collected  only 
on  properly-cut  filters  which  fit  closely  to  the  inner  surface 
of  the  funnel,  and  the  liquid  in  which  the  precipitate  is  sus- 
pended should  be  poured  down  a  glass  rod  into  the  filter. 
The  precipitates  should  be  thoroughly  washed  before  proceed- 
ing with  the  further  examination. 

Concentrated  solutions  should  be  diluted  with  water  before 
the  examination  is  commenced.  Solutions  containing  much 
free  acid  should  be  boiled  to  expel  the  excess  of  acid  and 
then  diluted  with  water  before  the  examination  is  commenced. 
This  dilution  may  cause  turbidity,  in  consequence  of  the  for- 
mation of  basic  salts  or  oxychlorides  of  bismuth,  antimony, 
or  mercury.  These,  however,  may  be  redissolved  by  the 
addition  of  a  little  nitric  or  hydrochloric  acid. 

The  filtrate,  including  the  wash-water,  from  each  group  pre- 
cipitation is  reserved  for  treatment  with  the  succeeding  group 
reagent.  If  no  precipitate  is  produced  by  a  group  reagent,  it 
indicates  that  the  metals  of  that  particular  group  are  absent. 
The  solution  is  then  treated  with  the  succeeding  group  reagent. 

FIRST    GROUP. 

(a)  Neutral  or  acid  solutions  are  treated  Avith  a  few  drops 
of  dilute  hydrochloric  acid. 
There  will  be  precipitated  : 

Silver,  as  white,  curdy  AgCl,  argentic  chloride. 
Mercury  (in  the  mercurous  condition),  as  white,  pulveru- 
lent HgCl,  mercurous  chloride. 
Lead,,  as  white  crystalline  PbClg,  plumbic  chloride. 
If  a  precipitate  is  produced,  it  is  collected  on  a  filter  and 


137 

examined  according  to  Sepamtion  of  the  First  Group,  page 
146.  The  filtrate,  or  the  solution  in  which  hydrochloric  acid 
failed  to  produce  a  precipitate,  is  treated  with  the  Second 
Group  reagent,  page  139. 

Lead  is  incompletely  precipitated,  as  it  is  slightly  soluble 
in  water ;  therefore  a  test  for  it  must  also  be  made  in  the 
second  group.  The  solution  in  which  the  precipitation  takes 
place  must  be  cold,  as  plumbic  chloride  is  easily  soluble  in 
hot  water  and  might  remain  in  solution ;  moreover,  small 
quantities  of  mercurous  salts  might  be  overlooked  in  the 
presence  of  nitric  acid,  as,  when  hydrochloric  acid  and  nitric 
acid  are  both  present  and  the  solution  is  warm,  mercurous 
chloride  is  transformed  into  soluble  mercuric  chloride. 

Furthermore,  it  should  be  observed  whether  the  precipitate 
redissolves  on  the  addition  of  an  excess  of  the  hydrochloric 
acid.  On  the  addition  of  dilute  hydrochloric  acid,  dilute 
solutions  of  compounds  of  bismuth  yield  a  white  precipitate 
of  BiOCl,  bismuth  oxychloride,  which  on  the  further  addition 
of  hydrochloric  acid  is  redissolved  as  BiClg,  bismuthous  chlo- 
ride. Compounds  of  antimony,  especially  K(SbO)C4H40g, 
potassium  antimonious  tartrate,  with  dilute  hydrochloric 
acid  form  SbOCl,  antimonious  oxychloride,  which  is  soluble 
in  an  excess  of  the  acid  as  SbClg,  antimonious  chloride. 
KHC^H^Og,  acid  potassium  tartrate,  if  it  should  have  sepa- 
rated, would  be  redissolved  on  the  further  addition  of  hydro- 
chloric acid : 

KHC^HA  +  HCl  =  H^C.HA  +KC1. 

Furthermore,  there  may  be  precipitated  in  the  first  group : 

boric  acid  (crystalline),  organic  acids,  and  sulphur.     (Sulphur 

separates  from  hyposulphites  and  polysulphides : 

Na^SA  +  2HC1  =  2NaCl  +  S  +  SO^  +  H^O ; 

(NHJ^Ss  -f  2HC1  =  2NH4CI  H-  S2  +  H2S. 

In  the  first  case  sulphurous  anhydride,  in  the  latter  case  hy- 

12* 


138 

drogen  sulphide,  is  evolved  with  the  sulphur.     Poly  sulphides 
are  always  alkaline  in  reaction.) 

Attention  should  be  paid  to  any  gases  evolved  on  treat- 
ment with  hydrochloric  acid  (with  reference  to  the  manner  of 
distinguishing  them  see  pages  116  to  119  and  121,  6.)  Sul- 
phurous anhydride  must  be  driven  off  by  heating;  other- 
wise, on  the  addition  of  hydrogen  sulphide,  separation  of 
sulphur  would  occur  (together  with  the  formation  of  pen- 
tath ionic  acid) : 

5SO2  +  5H2S  -=  H^SA  +  S5  +  4H2O. 
Chlorine,  nitrogen  dioxide,  etc.,  should  also  be  expelled  by 
heating  the  liquid. 

(b)  Alkaline  solutions  should  be  treated  with  hydrochloric 
acid  until  acid  in  reaction,  and  any  formation  of  precipitates 
or  evolution  of  gases  observed.  From  alkaline  solutions 
there  may  separate : 

1.  Sulphur  and  sulphides  of  the  metals,  accompanied  by 
the  evolution  of  hydrogen  sulphide. 

The  sulphides  are  the  following  sulpho-acids  :  AsgSg,  AsgSg, 
SbgSg,  Sb2S5,  SnS^ :  they  should  be  tested  according  to  the 
directions  given  in  the  chapter  treating  of  them  under  the 
second  group  (see  B,  page  152).  Under  certain  conditions 
CuS,  HgS,  and  NiS  might  also  be  encountered  at  this  stage. 
The  filtrate  from  the  sulphur  or  the  sulphides  which  have 
separated  may  be  examined  directly  for  the  metals  of  the 
fifth  and  sixth  groups. 

2.  Cyanides  of  the  heavy  metals  (which  were  dissolved  in 
cyanides  of  the  alkalies),  with  the  evolution  of  hydrocyanic 
acid.  Concentrated  hydrochloric  acid  is  added  to  the  liquid 
containing  the  precipitate  and  the  whole  heated.  The  cyanides 
are  thereby  converted  into  chlorides,  which  finally  dissolve, 
argentic  chloride  alone  remaining  undissolved.  The  solution 
is  then  examined  for  the  presence  of  metals  of  the  second, 


139 

third,  and  subsequent  groups;  argentic  chloride  in  the  residue 
is  confirmed  by  testing  its  solubility  in  ammonium  hydroxide. 

3.  Silicic  acid :  gelatinous ;  should  be  confirmed  in  the 
bead  of  microcosmic  salt  (see  4,  page  85).  The  solution, 
together  with  the  precipitate,  is  treated  with  an  excess  of 
hydrochloric  acid,  and  evaporated  to  dryness  on  the  water- 
bath  to  render  the  silicic  acid  insoluble.  The  residue  is 
extracted  with  water  and  a  little  hydrochloric  acid  (page 
130,  a),  and  the  filtrate  examined  for  bases.  It  usually 
contains  nothing  but  the  alkalies. 

4.  Precipitates  of  plumbic  hydroxide,  aluminium  hydrox- 
ide, chromium  hydroxide,  and  zinc  hydroxide  may  be  formed, 
but  on  acidifying  with  hydrochloric  acid  will  immediately 
disappear,  being  converted  into  soluble  chlorides. 

SECOND  GROUP. 

The  acid  filtrate  from  the  first  group  precipitate,  or  the 
solution  in  which  hydrochloric  acid  failed  to  produce  a  pre- 
cipitate, is  warmed  and  hydrogen  sulphide  conducted  into  the 
acid  solution  until  a  distinct  odor  of  the  gas  is  observable  in 
the  liquid. 

There  will  be  precipitated  : 

Lead,  as  black  PbS,  plumbic  sulphide. 
Mercury  (in  the  mercuric  condition),  as  black  HgS,  mer- 
curic sulphide. 
Copper,  as  black  CuS,  cupric  sulphide. 
Bismuth,  as  brownish-black  BigSg,  bismuthous  sulphide. 
Gold,  as  black  AujSg,  auric  sulphide. 
Platinum,  as  brownish-black  PtSa,  platinic  sulphide. 
Cadmium,  as  yellow  CdS,  cadmium  sulphide. 
Arsenious  compounds,  as  yellow  AS2S3,  arsenious  sulphide. 
Arsenic  compounds,  as  yellow  AsgSj,  arsenious  sulphide 
(with  sulphur). 


140 

Antimonious  compounds^  as  orange-red  SbgSg,  antimoni- 

ous  sulphide. 
Antlmonic   compounds,  as   omnge-red   SbgSg,  antimonic 

sulphide  (together  with  SbaSg  and  S). 
Stannous  compounds,  as  brownish-black  SnS,  stannous 

sulphide. 
Stannic  compounds,  as  yellow  SnSg,  stannic  sulphide. 
If  a  precipitate  is  produced,  it  is  collected  on  a  filter  and 
examined  according  to  Separation  of  the  Second  Group,  page 
148.  The  filtrate,  or  the  solution  in  which  hydrogen  sul- 
phide failed  to  produce  a  precipitate,  is  treated  with  the 
Third  Group  reagent,  page  141. 

From  solutions  containing  hydrochloric  acid,  when  hydro- 
gen sulphide  is  not  present  in  sufficient  quantity,  lead  is  pre- 
cipitated as  red  Pb2SCl2,  plumbic  sulphochloride,  which  is 
converted  by  further  addition  of  hydrogen  sulphide  into 
black  PbS.  In  solutions  of  mercuric  salts  white  precipitates 
of  double  salts  (for  example,  Hg3S3Cl2)  are  formed,  which  on 
continuing  the  addition  of  hydrogen  sulphide  become  yellow, 
then  brown,  and  finally  are  converted  into  black  HgS. 
Arsenious  acid  is  precipitated  at  once,  arsenic  acid  gradually ; 
the  precipitation  is  accelerated,  however,  by  heating  (see  1, 
page  34). 

Sulphur  may  also  separate  when  hydrogen  sulphide  is  intro- 
duced into  the  solution.     This  separation  may  be  caused  by  : 
1.  Chlorine,  bromine,  iodine,  nitrous  acid,  nitrogen  dioxide, 
etc.  (in  consequence  of  their  oxidizing  action  upon  hydrogen 
sulphide) ;  for  example  : 

Cl2  +  H2S-=2HCl  +  S; 

N2O3  +  H2S  =  2NO  +  H.O  -h  S. 

On  passing  hydrogen  sulphide  into  solutions  containing  an 

excess  of  nitric  acid  or  nitro-hydrochloric  acid,  sulphur  is 

separated.     The   excess   of    acid    should    be   driven    off  by 


141 

evapomtion  and,  after  diluting  with  water,  the  introduction 
of  hydrogen  sulphide  should  be  repeated. 

2.  Sulphurous  acid  (page  137). 

3.  Ferric  salts,  in  consequence  of  their  reduction  to  ferrous 
salts : 

2FeCl3  +  H^S  =-  2FeCl2  +  2HC1  +  S. 
Decolorization  of  the  solution  results  from  the  reduction. 

4.  Chromic  acid  and  chromates,  in  consequence  of  their 
reduction  to  chromic  salts  : 

2H2CrO,  +  3H2S  +  6HC1  =-2CrCl3+  SUfi  +  S3. 
The  solution  changes  in  color  from  yellow  to  green.  By 
repeated  introduction  of  hydrogen  sulphide  accompanied  by 
renewed  additions  of  hydrochloric  acid,  the  chromic  acid  is 
completely  decomposed.  If  the  acid  is  not  added  in  sufficient 
quantity,  a  precipitate  is  formed  consisting  either  of  green 
chromic  hydroxide : 

2H2CrO,  +  3H2S  =2Cr(OH)3+  S3  +  21Ifi, 
or  of  brown  chromium  chromate  : 

SH^CrO,  -h  3H2S  =  (CrO)2CrO,  +  S3  +  6Rfi. 

5.  Permanganic  acid  and  permanganates,  in  consequence 
of  their  reduction  to  manganous  compounds  : 

2HMnO,  +  5H2S  +  4HC1  =  2MnCl2  +  S^  +  SH^O. 
The  purplish-red  solution  is  decolorized.     The  procedure  is 
the  same  as  in  4,  page  141.     (If  the  hydrochloric  acid  is  not 
added  in  sufficient  quantity,  brown  precipitates  are  formed.) 


THIRD  GROUP. 

From  the  filtrate  of  the  second  group,  or  from  the  solution 
in  which  hydrogen  sulphide  failed  to  produce  a  precipitate, 
the  hydrogen  sulphide  is  expelled  by  boiling.  A  small 
quantity  of  nitric  acid  is  added  and  the  solution  warmed  to 
oxidize  the  bases,  ammonium  chloride  and  afterwards  ammo- 


142 

niiim  hydroxide  (the  latter  in  not  too  great  excess)  are  added, 
and  the  solution  is  boiled  until  the  odor  of  ammoniacal  gas 
can  no  longer  be  detected. 
There  will  be  precipitated  : 

Iroy}j  as  reddish-brown  Fe(OH)3,  ferric  hydroxide. 
Chromium,  as  bluish-green  Cr(OH)3,  chromic  hydroxide. 
Aluminium,   as  white   gelatinous  Al(OH)3,   aluminium 
hydroxide. 
In  the  presence  of  phosphoric  or  oxalic  acid, — 
Ferric  phosphate,  FePO^  (white). 
Alum,inium  phosphate,  AlPO^  (white). 
Phosphates  and  oxalates  of  cal-  \  Ca3(P04)2,  etc.  (white). 

eium,  strontium,  barium,  i  CaC204,  etc.  (white). 

Ammonium  magnesium  phosphate,  MgNH4P04  (white). 
If  a  precipitate  is  produced,  it  is  collected  on  a  filter  and 
examined  according  to  Separation  of  the  Third  Group,  page 
159.  The  filtrate,  or  the  solution  in  which  ammonium  hy- 
droxide failed  to  produce  a  precipitate,  is  treated  with  the 
Fourth  Group  reagent,  page  143. 

In  presence  of  iron  some  manganese  may  be  precipitated 

as  Mn(0H)2,  manganous  hydroxide. 
The  hydrogen  sulphide  must  be  expelled,  so  that,  on  the 
addition  of  the  ammonium  hydroxide,  ammonium  sulphide 
may  not  form  and  thereby  precipitate  the  fourth  group  with  the 
third.  By  means  of  the  nitric  acid  ferrous  salts  are  converted 
into  ferric  salts ;  in  presence  of  ammonium  chloride  the  fer- 
rous salts  are  not  precipitated,  or  are  precipitated  only  incom- 
pletely. If  the  oxidation  is  not  complete,  a  greenish  precip- 
itate is  obtained  in  the  presence  of  ferrous  salts,  which,  when 
exposed  to  the  air,  oxidizes  and  gradually  changes  to  black 
and  finally  to  reddish-brown  (ferric  hydroxide). 

In  solutions  containing  silicates  the  ammonium  hydrox- 
ide may  precipitate  gelatinous  HgSiOa,  silicic  acid.     H2SO1 


143 

may  possibly  be  formed  (by  the  oxidation  of  the  H2S  passed 
into  the  solution),  and  precipitate  barium  and  strontium  as 
sulphates.  Ammonium  chloride  is  added  to  prevent  the  pre- 
cipitation of  manganese  and  magnesium  (see  3,  page  56,  and 
1,  page  66).  The  ammonium  chloride  should  be  added  in 
excess, — but  not  too  great  excess,  as  thereby  the  precipitation 
of  the  fifth  group  is  unnecessarily  rendered  more  difficult. 
After  the  addition  of  the  ammonium  hydroxide  it  is  neces- 
sary to  boil  the  liquid  until  the  odor  of  ammonia  disappears, 
in  order  to  completely  precipitate  aluminium  and  chromium 
(see  1,  page  50,  and  1,  page  52).  By  this  procedure  the  excess 
of  ammoniacal  gas  is  expelled ;  but  the  boiling  should  not  be 
continued  too  long,  as  the  solution  may  become  acid  (in  con- 
sequence of  the  decomposition  of  NH4CI  with  the  liberation 
of  NH3). 

FOURTH  GROUP. 

To  the  filtrate  from  the  third  group  (to  which  ammonium 
hydroxide  is  again  added),  or  to  the  solution  in  which  ammo- 
nium hydroxide,  in  presence  of  ammonium  chloride,  failed 
to  produce  a  precipitate,  colorless  or  slightly  yellow  ammo- 
nium sulphide  is  added. 
There  will  be  precipitated  : 

Manganese,   as   light-salmon-colored   MnS,  manganous 

sulphide. 
Zinc,  as  white  ZnS,  zinc  sulphide. 
Nickelj  as  black  NiS,  nickelous  sulphide. 
Cobalt,  as  black  CoS,  cobaltous  sulphide. 
If  a  precipitate  is  produced,  it  is  collected  on  a  filter  and 
examined  according  to  Separation  of  the  Fourth  Group,  page 
164.     The  filtrate,  or  the  solution  in  which  ammonium  sul- 
phide  failed    tu    produce  a  precipitate,  is   treated  with   the 
Fifth  Group  reagent,  page  144. 


144 

Xickelous  sulphide  is  slightly  soluble  in  an  excess  of  yellow 
ammonium  sulphide,  imparting  a  brown  color  to  the  solution. 
The  nickelous  sulphide  is  completely  separated  on  boiling  the 
solution,  especially  after  the  addition  of  acetic  acid.  Ammo- 
nium sulphide  might  also  precipitate  iron  as  ferrous  sulphide, 
in  case  the  iron  were  held  in  solution  by  organic  substances. 

FIFTH  GROUP. 

From  the  filtrate  of  the  fourth  group,  or  from  the  solution 
in  which  ammonium  sulphide  failed  to  produce  a  precipitate, 
the  ammonium  sulphide  is  expelled  by  boiling,  any  sulphur 
which  may  have  separated  is  filtered  off,  ammonium  hydrox- 
ide and  ammonium  carbonate  are  added  to  the  filtrate,  and 
the  whole  is  boiled  as  long  as  carbon  dioxide  is  evolved. 

There  will  be  precipitated  : 

Barium,  as  white  BaCOg,  barium  carbonate. 
Strontium,  as  white  SrCOg,  strontium  carbonate. 
Cahdum,  as  white  CaCOg,  calcium  carbonate. 

If  a  precipitate  is  produced,  it  is  collected  on  a  filter  and 
examined  according  to  Separation  of  the  Fifth  Group,  page 
165.  The  filtrate,  or  the  solution  in  which  ammonium  car- 
bonate failed  to  produce  a  precipitate,  is  examined  according 
to  the  directions  given  under  Separation  of  the  Sixth  Group, 
page  168. 

On  the  addition  of  commercial  ammonium  carbonate,  acid 
carbonates  soluble  in  water — as,  for  example,  Ca(HC03)2 — 
are  produced  (page  62),  which,  on  boiling,  are  converted  into 
neutral,  insoluble  carbonates,  with  the  liberation  of  COg  and 
H,0: 

Ca(HC03)2  =  CaCOj  +  CO2  +  H2O. 
The  carbonates  are  soluble  in  an  excess  of  ammonium  chlo- 
ride on  long-continued  boiling : 

CaCOa  +  2NH,C1  =  CaCl^  +  2NH3  +  CO2  +  Hp. 


145 


SIXTH  GROUP. 


In  this  group  are  classed  magnesium,  potassium,  sodium, 
and  lithium.  Ammonium  is  also  classed  with  this  group, 
but  the  test  for  it  must  be  made  in  the  original  substance 
presented  for  analysis. 

(With  reference  to  their  separation  see  Separation  of  the 
Sixth  Group,  page  168.) 

With  this  group  may  also  be  found  the  ferro-  and  ferri- 
cyanides  of  the  alkalies,  cobalticyanides  of  the  alkalies,  etc., 
from  which  the  iron  and  cobalt  are  not  precipitated  by  the 
ordinary  reagents.  Furthermore,  aluminium  may  have  re- 
mained in  solution,  because  of  the  presence  of  organic  sub- 
stances. These  compounds  are  to  be  treated  with  concen- 
trated sulphuric  acid  (page  130)  and  separated  by  the  regular 
group  precipitations. 


13 


146 


SEPARATION  OF  THE   BASES  CONTAINED   IN 
THE  GROUP  PRECIPITATES. 

The  group  precipitates  thus  obtained  are  now  examined 
separately.  The  precipitates  of  the  second  and  fourth  groups 
must  be  examined  immediately,  as  they  oxidize  when  exposed 
to  the  air.  Precipitates  of  the  third  group  must  be  quickly 
filtered,  in  order  to  prevent  the  formation  and  precipitation 
of  manganic  hydroxide ;  for  example  : 

2(NH,)2MnCl,  +  4NH,OH  +  Hp  +  O  -^  Mn^COH),  + 
8NH4CI. 
If  no  precipitate  is  formed  in  the  third  group,  ammonium 
sulphide  should  be  added  rapidly,  to  prevent  the  separation 
of  manganic  hydroxide.  If  arsenic  or  tin  be  founa  in  the 
second  group,  a  portion  of  the  filtrate  is  reserved  for  the  tests 
for  acids  and  the  other  portion  is  used  in  testing  for  bases. 

The  filtrate,  including  the  wash-water,  from  each  group 
precipitation  is  reserved  for  treatment  with  the  succeeding 
group  reagent.  If  no  precipitate  is  produced  by  a  group 
reagent,  it  indicates  that  the  metals  of  that  particular  group 
are  absent.  The  solution  is  then  treated  with  the  succeeding 
group  reagent. 

SEPARATION  OF  THE  FIRST  GROUP. 

The  precipitate  produced  by  hydrochloric  acid  (page  137) 
is  collected  on  a  filter  and,  after  having  been  washed  with 
cold  water,  is  treated  while  on  the  filter  with  hot  water ;  any 
plumbic  chloride  present  is  dissolved  by  the  hot  water,  and 
may  be  tested  for  in  the  cooled  filtrate  by  the  addition  of 


147 

sulphuric  acid ;  the  formation  of  a  white  precipitate  of  PbSO^ 
indicates  the  presence  of  lead.  Argentic  chloride  and  mer- 
curous  chloride  would  remain  on  the  filter,  undissolved  by 
the  hot  water.  Any  residue  remaining  on  the  filter  is 
washed  with  hot  water  until  free  from  lead  (test  washings 
with  sulphuric  acid,  provided  lead  has  been  found),  and  then 
treated,  while  on  the  filter,  with  ammonium  hydroxide :  mer- 
curous  chloride  is  converted  into  black,  insoluble  NHgHggCl, 
dimercurous  ammonium  chloride,  indicating  the  presence  of 
mercury  in  the  mercurous  condition,  while  argentic  chloride 
is  dissolved  by  the  ammonium  hydroxide  as  Ag(NH3)2Cl, 
argent-ammonium  chloride,  and  passes  through  the  filter  with 
the  filtrate  into  the  vessel  below.  The  ammoniacal  filtrate 
is  treated  with  nitric  acid  until  acid  in  reaction.  A  white 
precipitate  of  AgCl  indicates  the  presence  of  silver. 

To  detect  small  quantities  of  argentic  chloride  in  the  pres- 
ence of  mercurous  chloride,  the  dry  mixture  of  the  chlorides 
is  heated  in  a  small  glass  tube  :  mercurous  chloride  will  vola- 
tilize, while  argentic  chloride  remains  as  a  horn-like  mass, 
which  may  be  further  tested  on  charcoal  with  the  blowpipe. 


148 


TABLE  II.— SEPARATION  OF  THE  FIRST  GROUP. 
The  precipitate,  which  may  contain  AgCl,  HgCl,  PbCl,,  is  treated,  while 
on  the  filter,  with  hot  water. 


CooUd  Filtrate. 

PbClj. 

Treat  with  HjSO^ : 

Insoluble  Residue. 

AgCl,  HgCl. 

Treat  with  ammonium  hydroxide  : 

white  precipitate  of  PbSO^  indi- 
cates presence  of  lead. 

Filtrate. 

Residue. 

Ag 
(as  Ag(NH3),Cl). 
Treat  with  HNO3: 

Hg 
as  black 
NH^HgjCl     indi- 

white,  curdy  pre- 
cipitate of  AgCl 
indicates       pres- 

cates presence  of 
mercurous  salts. 

ence  of  silver. 

SEPARATION  OF  THE  SECOND  GROUP. 

Of  the  sulphides  of  the  second  group  some  are  basic  and 
others  acid  in  character ;  therefore  some  of  them  are  unacted 
upon  by  ammonium  sulphide,  while  others  are  dissolved  as 
sulpho-salts. 


BoMC  Sulphides — Insoluble. 

Lead  sulphide. 
Mercuric  sulphide. 
Cupric  sulphide. 
Bismuthous  sulphide. 
Cadmium  sulphide. 


Acid  Sulphides — Soluble. 

Arsenious  sulphide. 
Antimonious  sulphide. 
Antimonic  sulphide. 
Stannous  sulphide. 
Stannic  sulphide. 
Auric  sulphide. 
Platinic  sulphide. 


(Cupric  sulphide  is  slightly  soluble  in  ammonium  sulphide,  insoluble, 
however,  in  sodium  sulphide  and  in  potassium  sulphide.  Mercuric  sul- 
phide is  insoluble  in  ammonium  sulphide,  but  soluble  in  sodium  sulphide 
and  in  potassium  sulphide  containing  free  alkali.  Stannous  sulphide  is 
insoluble  in  colorless  ammonium  sulphide,  but  easily  soluble  in  yellow 
ammonium  sulphide.) 


149 

I.  To  ascertain  whether  sulphides  of  both  basic  and  acid 
divisions  or  of  only  one  division  are  present,  the  precipitate 
produced  by  hydrogen  sulphide  (page  139)  is  collected  on  a 
filter,  washed,  and  then  examined  regarding  its  behavior  with 
ammonium  sulphide.  For  this  purpose  a  small  portion  of 
the  precipitate  is  taken  from  the  filter,  placed  in  a  test-tube, 
treated  with  ammonium  hydroxide  and  then  with  yellow 
ammonium  sulphide,  and  slightly  warmed,  any  residue  re- 
maining undissolved  is  filtered  off,  and  the  filtrate  is  acidified 
with  dilute  hydrochloric  acid,  to  ascertain  whether  a  sulpho- 
salt  is  present  in  the  solution, — that  is,  whether  a  (colored) 
precipitate  of  a  sulphide  is  formed. 

(a)  If,  on  the  addition  of  dilute  hydrochloric  acid  to  the 
filtrate  no  precipitate  appears,  or  only  a  milkiness  due  to 
the  separation  of  sulphur  from  the  yellow  ammonium  sul- 
phide is  produced,  none  of  the  sulphides  have  entered  into 
solution  in  the  ammonium  sulphide,  and,  therefore,  basic  sul- 
phides only  are  present.  Consequently  the  remainder  of  the 
precipitate  produced  by  hydrogen  sulphide  should  be  treated 
according  to  directions  given  under  A,  page  150. 

(6)  If  the  precipitate  is  completely  dissolved  by  the  am- 
monium sulphide,  acid  sulphides  only  are  present,  and  the 
remainder  of  the  precipitate  produced  by  hydrogen  sulphide 
should  be  examined  according  to  B,  II.,  page  152. 

(c)  If  a  portion  of  the  precipitate  remain  undissolved  and 
another  portion  enter  into  solution  in  ammonium  sulphide,  as 
shown  by  the  production  of  a  colored  precipitate  on  acidi- 
fying the  ammonium  sulphide  filtrate  with  dilute  hydro- 
chloric acid  as  before  described  (I.,  page  149),  the  entire  re- 
mainder of  the  precipitate  produced  by  hydrogen  sulphide  is 
treated  with  ammonium  hydroxide  and  ammonium  sulphide, 
warmed,  the  insoluble  part  filtered  off  and  examined  accord- 
ing to  a,  page  150,  while  the  solution  (filtrate)  is  treated  ac- 

13* 


150 

cording  to  I.,  page  162,  or,  if  the  presence  of  gold  or  plati- 
num is  suspected,  according  to  C,  page  1 54. 

A.    FURTHER   SEPARATION   OF   THE   BASIC   SULPHIDES. 

(a)  The  thoroughly  washed  precipitate  of  the  basic  sul- 
phides is  taken  from  the  filter,  placed  in  a  porcelain  dish,  and 
boiled  with  dilute  nitric  acid  (adding  fresh  portions  of  water 
to  replace  that  lost  by  evaporation)  until  no  further  change 
takes  place  in  the  precipitate.  Lead,  bismuth,  copper,  and  cad- 
mium will  enter  into  solution  as  nitrates ;  mercuric  sulphide 
remains  insoluble  as  a  heavy  black  powder.  The  mercuric 
sulphide  is  filtered  off  and  examined  according  to  c,  page 
150,  and  the  filtrate  is  examined  according  to  d,  page  151. 

(6)  If  the  precipitate  of  sulphides  is  completely  dissolved 
by  the  dilute  nitric  acid  (with  the  exception  of  sulphur,  which 
floats  on  the  surface  of  the  liquid),  mercury  was  not  present. 
Complete  solution  having  taken  place,  the  nitric  acid  solution 
is  examined  according  to  c?,  page  151. 

(c)  The  mercuric  sulphide*  on  the  filter  is  washed,  removed 
from  the  filter,  placed  in  a  porcelain  dish,  and  treated  with 
nitrohydrochloric  acid,  which,  on  being  heated,  dissolves  and 
converts  the  mercuric  sulphide  into  mercuric  chloride.  After 
evaporating  the  excess  of  acid  and  diluting  with  water,  this 


1  White  PbSO^  (see  4,  p.  20,  and  6,  p.  21)  as  well  as  white  Hg3S2(N03)2 
(see  4,  page  18)  may  be  precipitated  with  the  mercuric  sulphide.  Should 
this  occur,  the  precipitate  is  treated  with  ammonium  acetate,  which  dis- 
solves the  plumbic  sulphate,  and  if  an  insoluble  residue  remain,  the  liquid 
is  filtered.  The  presence  of  lead  in  the  filtrate  may  be  shown  by  the  for- 
mation of  a  yellow  precipitate  of  plumbic  chromate  on  the  addition  of 
acetic  acid  and  potassium  chromate.  The  insoluble  residue  on  the  filter  is 
dissolved  in  nitro-hydrochloric  acid,  the  excess  of  acid  expelled  by  evapo- 
ration, the  solution  diluted  with  water  and  tested  for  mercury  with  stan- 
nous chloride.  The  production  of  a  grayish  precipitate  indicates  the 
presence  of  mercury. 


151 

solution  yields  with  stannous  chloride  a  white  precipitate  of 
HgCl,  or  a  gray  precipitate  of  metallic  mercury. 

{d)  The  excess  of  acid  is  evaporated  from  the  nitric  acid  so- 
lution obtained  as  before  described,  the  solution  diluted  with  a 
small  quantity  of  water,  and  then  treated  with  dilute  sulphuric 
acid :  lead  is  precipitated  as  white  plumbic  sulphate.  The 
plumbic  sulphate  is  filtered  oflF,  and  the  filtrate,  or  the  solu- 
tion in  which  sulphuric  acid  failed  to  produce  a  precipitate,  is 
treated  with  an  excess  of  ammonium  hydroxide.  If  bismuth 
is  present  a  white  precipitate  of  BiO-OH,  bismuth  hydroxide, 
insoluble  in  an  excess  of  the  reagent,  is  produced.  As  a  con- 
firmatory test  the  precipitate  should  be  collected  on  a  filter  and 
dissolved  in  dilute  hydrochloric  acid ;  if,  on  adding  the  solu- 
tion to  a  large  quantity  of  water,  a  separation  of  white  bismuth 
oxy chloride  takes  place,  the  presence  of  bismuth  is  fully  estab- 
lished. Copper  and  cadmium  are  also  precipitated  by  ammo- 
nium hydroxide,  but  redissolve  in  an  excess  of  the  reagent. 
If  the  solution  is  colored  blue,  copper  is  present.  To  test  for 
cadmium  the  solution  is  decolorized  by  potassium  cyanide,  and 
hydrogen  sulphide  conducted  into  the  liquid ;  a  yellow  pre- 
cipitate of  CdS  indicates  the  presence  of  cadmium.  If  the 
ammoniacal  solution  is  colorless,  it  is  treated  directly  with 
hydrogen  sulphide  to  ascertain  whether  a  precipitate  of 
yellow  cadmium  sulphide  is  produced. 

(As  plumbic  sulphate  is  soluble  in  concentrated  nitric  acid 
and  also  in  salts  of  ammonium,  it  might  be  overlooked  in  the 
presence  of  an  excess  of  nitric  acid  or  in  consequence  of  the 
incomplete  elimination  of  ammonium  sulphide  (before  dis- 
solving in  nitric  acid),  and  thus  interfere  with  the  tests  for 
other  substances.  At  the  point  v/here  bismuth  is  precipitated 
by  ammonium  hydroxide,  ferric  hydroxide,  aluminium  hy- 
droxide, etc.,  may  also  be  precipitated,  especially  if  the  original 
precipitate  produced  by  hydrogen  sulphide  has  not  been  suffi- 
ciently  washed.     With   copper   may  be   found   nickel   and 


152 

cobalt;  with  cadmium,  zinc.     Plumbic  hydroxide  might  also 
be  precipitated  here  by  ammonium  hydroxide.) 

B.    FURTHER  SEPARATION   OF   ACID   SULPHIDES. 

I.  The  ammonium  sulphide  solution  may  contain  the  sul- 
pho-salts  (NHJgAsS^,  (NH,)3SbS„  (NH,)2SnS3,  and  may  yield 
on  the  addition  of  hydrochloric  acid  a  yellow  or  orange-red 
precipitate  of  AsgSg,  SbaSg,  SnSg.  If  no  precipitate,  or  only 
a  milkiness,  due  to  the  separation  of  sulphur  from  the  am- 
monium sulphide,  is  produced,  it  indicates  the  absence  of 
sulphides  of  arsenic,  antimony,  and  tin.  (Any  black  SnS 
which  may  have  been  present  originally  would  be  precipitated 
here  as  yellow  SnSa ;  see  1,  page  41.) 

II.  The  colored  precipitate  of  acid  sulphides  is  collected 
on  a  filter  and  thoroughly  washed.  The  separation  of  the 
three  sulphides  may  be  accomplished  by  either  of  two  methods, 
— by  hydrochloric  acid  or  by  ammonium  carbonate.  The 
separation  by  ammonium  carbonate  is  preferable  in  case  the 
preliminary  examination  indicated  the  presence  of  arsenic. 

A.  Separation  by  Hydrochloric  Acid. — (a)  The  remainder 
of  the  precipitate  of  sulphides,  a  portion  of  which  was  found 
to  be  completely  soluble  in  ammonium  sulphide,  or  the  pre- 
cipitate obtained  by  the  addition  of  hydrochloric  acid  to  the 
ammonium  sulphide  solution  (after  having  been  pressed  be- 
tween sheets  of  filter  paper  to  remove  the  excess  of  moisture), 
is  treated  with  concentrated  hydrochloric  acid  and  warmed : 
antimony  and  tin  enter  into  solution  as  chlorides,  while 
arsenic  sulphide  and  sulphur  remain  undissolved.  (Cupric 
sulphide  would  also  be  dissolved  by  the  hydrochloric  acid. 
A  test  for  it  may  be  made  by  treating  a  few  drops  of  the 
solution  with  ammonium  hydroxide ;  the  production  of  a 
blue  coloration  indicates  the  presence  of  copper.) 

(b)  To  test  for  antimony,  a  few  drops  of  the  hydrochloric 


153 

acid  solution  are  placed  on  platinum  foil  and  a  small  piece  of 
zinc  is  placed  in  the  liquid.  If  antimony  is  present,  a  black 
deposit  of  metallic  antimony  is  formed  which  adheres  to  the 
platinum  foil.  To  test  for  tin  which  may  be  present  as 
stannic  chloride,  a  fragment  of  metallic  zinc  is  placed  in  the 
remainder  of  the  hydrochloric  acid  solution ;  if  both  tin  and 
antimony  are  present,  they  are  precipitated  as  a  spongy 
metallic  mass.  When  the  precipitation  is  complete,  the  super- 
natant liquid  containing  zinc  chloride  is  poured  off  and  the 
metallic  powder  remaining  is  treated  with  moderately  concen- 
trated hydrochloric  acid,  which  dissolves  the  tin  as  stannous 
chloride,  leaving .  the  antimony  undissolved.  The  antimony 
is  removed  by  filtration,  and  the  solution  of  stannous  chloride 
thus  obtained  yields  with  mercuric  chloride  a  precipitate  of 
either  white  mercurous  chloride  or  of  gray  metallic  mercury 
(see  4,  page  42).  On  dissolving  the  sulphides  in  hydrochloric 
acid,  arsenic  sulphide  (together  with  sulphur)  remains  undis- 
solved. To  confirm  the  presence  of  arsenic,  the  arsenic  sul- 
phide is  dissolved  in  warm  concentrated  nitric  acid,  the  solu- 
tion evaporated  to  dryness  on  a.  water-bath,  and  the  residue, 
containing  arsenic  acid,  dissolved  in  water.  Ammonium 
chloride,  ammonium  hydroxide,  and  magnesium  sulphate  are 
then  added,  to  ascertain  whether  crystalline  MgNH^AsO^, 
ammonium  magnesium  arseniate,  is  precipitated.  The  precipi- 
tate is  always  crystalline :  in  very  dilute  solutions  it  forms 
only  after  standing  some  time. 

B.  Separation  by  Ammonium  Carbonate. — If  the  remainder 
of  the  precipitate  of  sulphides,  or  the  preci[)itatc  obtained  by 
the  addition  of  hydrochloric  acid  to  the  ammonium  sulphide 
solution,  is  supposed  io  contain  much  arsenic  sulphide,  it  is 
collected  on  a  filter,  thoroughly  washed  with  water,  and  then 
digested  with  a  concentrated  solution  of  ammonium  carbonate. 
Arsenic  sulphide  enters  into  solution  (see  page  29),  while 


154 

SbaSg,  antimonic  sulphide,  and  SnSg,  stannic  sulphide,  remain 
undissolved,  and  after  being  collected  on  a  filter  and  washed 
are  dissolved  in  hydrochloric  acid  and  separated  according  to  6, 
page  152.  The  ammonium  carbonate  solution  of  arsenic  sul- 
phide is  evaporated  to  dryness  on  a  water-bath,  and  the  residue 
treated  with  concentrated  nitric  acid  to  oxidize  the  arsenic  to 
arsenic  acid.  The  solution  is  again  evaporated  to  dryness,  the 
residue  dissolved  in  water,  and  the  arsenic  precipitated  with 
magnesia  mixture  as  MgNH^AsO^,  as  under  h,  p.  152.  (To 
determine  whether  the  arsenic,  antimony,  or  tin  existed  in 
the  ic  or  ous  conditions,  see  the  pages  treating  of  the  special 
reactions  of  these  metals.  It  is,  of  course,  understood  that, 
in  testing  for  arsenic  acid  in  the  presence  of  phosphoric  acid, 
hydrogen  sulphide  is  the  only  reagent  that  can  be  employed.) 

C.     FURTHER    SEPARATION     OF     ACID     SULPHIDES     IF     THE 
PRESENCE   OF   GOLD   OR   PLATINUM    IS   SUSPECTED. 

The  ammonium  sulphide  solution  may  contain  the  sulpho- 
salts  (NHJaAsS,,  (NH,)3SbS„  (NH,)2SnS3,  (NHJgAuSa, 
(NH4)2PtS3,  and  may  yield  on  the  addition  of  hydrochloric 
acid  a  yellow,  orange-red,  or  brownish-black  precipitate  of 
AS2S5,  SbgSg,  SnSg,  Au2S3,PtS2.  If  no  precipitate,  or  only  a 
milkiness  (due  to  the  separation  of  sulphur  from  the  ammo- 
nium sulphide),  is  produced  on  adding  the  hydrochloric  acid, 
it  indicates  the  absence  of  sulphides  of  arsenic,  antimony,  tin, 
gold,  and  platinum.  The  colored  precipitate  is  collected  on  a 
filter,  thoroughly  washed,  dried,  and  then  mixed  with  twice 
its  bulk  of  a  dry  mixture  consisting  of  equal  parts  of  sodium 
carbonate  and  potassium  nitrate.  This  mixture  is  introduced, 
in  small  portions  at  a  time,  into  a  porcelain  crucible  contain- 
ing two  parts  (compared  with  the  quantity  of  precipitate)  of 
potassium  nitrate,  which  is  kept  just  at  the  point  of  fusion. 
The  temperature  must  not  be  of  such  a  degree  as  to  decom- 
pose the  potassium  nitrite  resulting  from  the  fusion  of  the 


155 

potassium  nitrate,  as,  when  the  precipitate  is  added,  sodium 
stannate  instead  of  stannic  oxide  may  be  formed.  When  cool, 
the  fused  mass  is  extracted  with  water  containing  alcohol  and 
filtered.  Any  insoluble  residue  is  treated  according  to  a, 
page  155.  The  alcohol  is  evaporated  from  the  filtrate,  which 
may  contain  arsenic,  and  then  ammonium  hydroxide,  ammo- 
nium chloride,  and  magnesium  sulphate  are  added.  A  white 
crystalline  precipitate  of  ammonium  magnesium  arseniate, 
which  may  appear  immediately  or  after  some  time,  indicates 
the  presence  of  arsenic. 

(a)  The  residue,  insoluble  in  alcohol,  which  may  contain 
metallic  gold  and  platinum,  stannic  oxide,  and  sodium  pyro- 
antimoniate,  is  boiled  with  a  concentrated  soluti  ^n  of  sodium 
hydroxide,  diluted  with  water,  and  filtered.  Any  insoluble 
residue  is  treated  according  to  6,  page  155.  The  filtrate, 
which  may  contain  tin  as  sodium  stannate,  is  acidulated  with 
hydrochloric  acid,  concentrated  by  evaporation,  and  a  piece  of 
metallic  zinc  placed  in  the  solution  to  precipitate  the  tin 
The  precipitate  is  collected  on  a  filter,  dissolved  in  hydro- 
chloric acid,  and  mercuric  chloride  added  to  the  solution.  The 
production  of  a  white  precipitate  of  mercurous  chloride  or 
gray  metallic  mercury  indicates  the  presence  of  tin. 

(b)  The  residue,  insoluble  in  sodium  hydroxide,  which  may 
contain  gold,  platinum,  and  sodium  pyroantimonate,  is  boiled 
with  concentrated  hydrochloric  acid,  slightly  diluted  with 
water,  and  then  filtered.  A  portion  of  the  filtrate,  which 
may  contain  antimonious  chloride,  is  placed  on  platinum  foil 
and  a  fragment  of  metallic  zinc  placed  in  it.  The  production 
on  the  platinum  of  a  brown  or  black  adherent  coating  indi- 
cates the  presence  of  antimony. 

The  residue  insoluble  in  concentrated  hydrochloric  acid, 
which  may  contain  metallic  gold  and  platinum,  is  dissolved 
by  heating  with  nitro-hydrochloric  acid,  the  solution  eva\x)- 
rated  to  dryness  on  a  water-bath,  the  residue  dissolved  in 


156 

water,  and  the  solution  boiled  with  ferrous  sulphate  and  then 
filtered.  The  insoluble  residue  of  gold  on  the  filter  is  fused 
on  charcoal  with  the  blowpipe  to  obtain  the  gold  in  the  form 
of  a  yellow  metallic  globule. 

The  filtrate,  which  may  contain  platinic  chloride,  is  heated, 
and,  while  hot,  hydrogen  sulphide  is  passed  into  the  solution. 
The  precipitate  is  collected  on  a  filter,  dissolved  by  heating 
with  nitro-hydrochloric  acid,  and  evaporated  to  dryness  on  a 
water-bath.  The  residue  is  dissolved  in  a  small  quantity  of 
water,  placed  in  a  watch-glass,  ammonium  chloride  added, 
and  the  liquid  stirred  with  a  glass  rod.  A  yellow,  crystalline 
precipitate  of  ammonium  chlorplatinate  indicates  the  pres- 
ence of  platinum. 


157 


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159 


SEPARATION  OF  THE  THIRD  GROUP. 

Before  proceeding  with  the  separation  of  the  members  of 
the  third  group,  the  presence  or  absence  of  phosphoric  acid 
(phosphates)  and  of  oxalic  acid  (oxalates)  in  the  precipitate 
produced  by  the  group  reagent,  ammonium  hydroxide, 
should  be  ascertained,  because  their  presence  or  absence  will 
determine  which  method  of  separation  shall  be  employed. 
To  obtain  this  information  the  procedure  should  be  that 
described  under  B,  page  160. 

The  test  for  phosphates  and  for  oxalates  need  be  made  in 
this  group  only  when  the  original  substance  was  dissolved  in 
acid  or  when  solutions  having  an  acid  reaction  are  presented 
for  analysis. 

If  the  group  precipitate  did  not  contain  phosphoric  acid 
or  oxalic  acid,  the  separation  of  the  members  of  the  group 
should  be  made  according  to  the  method  described  under  A, 
page  159.  If,  however,  the  group  precipitate  contained 
phosphoric  acid  or  oxalic  acid,  or  both,  the  separation  of  the 
members  of  the  group  should  be  made  according  to  «,  or  6, 
or  c,  pages  161  and  162,  dependent  upon  whether  phosphoric 
acid  or  oxalic  acid,  or  both,  are  present. 

A.  The  thoroughly  washed  precipitate  produced  by  am- 
monium hydroxide  is  removed  from  the  filter,  placed  in  a 
porcelain  dish,  covered  with  sodium  hydroxide,  bromine 
water  added,  and  slightly  warmed  for  about  five  minutes.<^> 
A  reddish-brown,  insoluble  residue  of  ferric  hydroxide   re- 


'  It  is  necessary,  during  this  treatment,  that  the  liquid  should  contain 
an  excess  of  sodium  hydroxide,  which  may  be  determined  by  rubbing  a 
drop  of  the  liquid  between  the  fingers  and  observing  whether  or  not  a 
slippery  sensation  is  produced  ;  the  reaction  with  turmeric  or  litmus  paper 
is  in  this  case  of  no  value,  as  NagAlO,  and  NagCrO,,  which  may  be 
formed  here,  are  also  alkaline  in  reaction.  The  production  of  a  slippery 
sensation  indicates  the  presence  of  an  excess  of  sodium  hydroxide. 


160 

maining  after  this  treatment  indicates  the  presence  of  iron. 
The  liquid  is  filtered,  and  the  filtrate  (or  the  solution  in 
which  sodium  hydroxide  may  have  failed  to  produce  a  pre- 
cipitate) is  treated  according  to  a,  page  160.  The  reddish- 
brown  residue  of  ferric  hydroxide  is  washed  with  water,  dis- 
solved in  hydrochloric  acid,  the  solution  diluted  with  water, 
and  the  presence  of  iron  confirmed  by  the  addition  of  potas- 
sium ferrocyanide ;  the  production  of  a  blue  precipitate  con- 
firms the  presence  of  iron. 

(a)  The  filtrate  from  the  reddish-brown  residue  of  ferric 
hydroxide  is  treated  with  an  excess  of  ammonium  chloride 
and  warmed  until  the  odor  of  ammonia  is  no  longer  percep- 
tible; the  formation  of  a  white,  gelatinous  precipitate  of 
aluminium  hydroxide  indicates  the  presence  of  aluminium. 
The  precipitate  of  aluminium  hydroxide  is  filtered  off  and 
the  filtrate  is  acidified  with  hydrochloric  acid  and  treated 
with  an  excess  of  hydrogen  sulphide,  the  solution  is  warmed 
several  minutes,  ammonium  hydroxide  is  added,  the  liquid  is 
again  heated,  and  if  chromium  be  present  it  will  separate  as  a 
bluish-gray,  gelatinous  precipitate  of  chromium  hydroxide, 
which  may  be  confirmed  by  its  imparting  an  emerald  color 
to  a  bead  of  borax. 

B.  If  the  original  solution  contained  phosphoric  or  oxalic 
acids,  the  group  reagent,  ammonium  hydroxide,  would  pre- 
cipitate the  members  of  the  third  group,  namely,  iron,  alu- 
minium, and  chromium  as  hydroxides  and  phosphates,  and 
the  alkaline  earths,  namely,  barium,  calcium,  strontium,  and 
magnesium,  were  they  present  in  the  original  solution,  as 
phosphates  and  oxalates.  Therefore,  a  preliminary  examina- 
tion of  the  precipitate  produced  by  ammonium  hydroxide  to 
ascertain  whether  or  not  phosphoric  or  oxalic  acids  are  present 
should  invariably  be  made  before  proceeding  with  the  separa- 


161 

tion  of  the  members  of  the  group.  For  this  purpose,  separate 
portions  of  the  precipitate  produced  by  the  group  reagent,  am- 
monium hydroxide,  are  examined  according  to  the  following 
methods : 

I.  A  portion  of  the  precipitate  is  boiled  with  an  excess  of 
sodium  carbonate.  The  liquid  is  filtered,  the  filtrate  acidified 
with  acetic  acid,  and  calcium  chloride  is  added.  The  pro- 
duction of  a  white,  pulverulent  precipitate  of  calcium  oxalate 
indicates  the  presence  of  oxalic  acid. 

II.  A  second  portion  of  the  precipitate  is  dissolved  in 
nitric  acid,  ammonium  molybdate  added,  and  the  solution 
warmed.  The  production  of  a  yellow  crystalline  precipitate 
of  ammonium  phosphomolybdate  indicates  the  presence  of 
phosphoric  acid. 

(a)  If  oxalic  acid  alone  is  present,  the  remaining  portion 
of  the  precipitate  produced  by  ammonium  hydroxide  is  re- 
moved from  the  filter,  placed  in  a  porcelain  crucible,  or  on  a 
piece  of  platinum  foil,  dried,  and  then  gently  ignited  to  de- 
stroy the  oxalic  acid.  The  residue  is  dissolved  in  hydro- 
chloric acid,  the  solution  diluted  with  water,  and  ammonium 
hydroxide  added  until  the  odor  of  ammonia  is  perceptible. 
The  precipitate,  which  will  consist  of  the  bases  which  were 
originally  in  combination  with  the  oxalic  acid,  is  examined 
according  to  A,  page  159. 

(6)  If  2)hosphoric  acid  alone  is  present,  the  precipitate  pro- 
duced by  ammonium  hydroxide  is  dissolved  in  hydrochloric 
acid.  A  small  portion  of  the  solution  is  diluted  with  water, 
and  potassium  ferrocyanide  is  added.  The  production  of  a 
blue  precipitate  indicates  the  presence  of  iron.  Ferric  chlo- 
ride is  added  to  the  remainder  of  the  solution  until  a  drop 
of  the  solution  placed  in  a  porcelain  dish  and  treated  with 
ammonium  hydroxide  yields  a  reddish-brown  precipitate. 
The  solution  is  nearly  neutralized  with  sodium  carbonate, 
I  14* 


162 

an  excess  of  sodium  acetate  is  added,  the  solution  boiled  for 
several  minutes  until  a  reddish-brown  precipitate  is  pro- 
duced, and  the  liquid  is  then  filtered  while  hot.  The  filtrate 
may  contain  the  alkaline  earths,  and  should  be  treated  with 
ammonium  hydroxide  and  ammonium  carbonate,  and  any 
precipitate  produced  examined  according  to  Separation  of  the 
Fifth  group,  page  165. 

The  reddish-brown  precipitate  produced  by  boiling  the 
solution  with  sodium  acetate  may  consist  of  ferric  phosphate, 
basic  ferric  acetate,  and  chromium  and  aluminium  phos- 
phates and  hydroxides.  The  precipitate  is  dissolved  in  hy- 
drochloric acid,  the  solution  is  cooled,  and  an  excess  of 
sodium  hydroxide  is  added,  thereby  precipitating  reddish- 
brown  ferric  hydroxide  resulting  from  the  ferric  chloride 
previously  added.  The  filtrate,  which  may  contain  alu- 
minium and  chromium  as  phosphates  and  hydroxides,  is 
boiled,  whereupon  chromium,  if  present,  will  separate  as  a 
bluish-gray  precipitate  of  chromium  phosphate  or  of  chro- 
mium hydroxide,  which  is  collected  on  a  filter  and  the 
presence  of  chromium  confirmed  by  its  imparting  an  emerald 
color  to  a  borax  bead.  The  filtrate  is  acidified  with  acetic 
acid,  and  if  aluminium  be  present  in  the  solution  as  a  phos- 
phate, it  will  separate  as  a  white,  gelatinous  precipitate.  If 
no  precipitate  should  appear  on  acidifying  the  solution  with 
acetic  acid,  excess  of  ammonium  hydroxide  is  added  and  the 
solution  is  warmed.  The  production  of  a  white,  gelatinous 
precipitate  of  aluminium  hydroxide  indicates  the  presence  of 
aluminium. 

(c)  If  both  oxalic  and  phosphoric  adds  are  present,  the  pre- 
cipitate is  detached  from  the  filter,  placed  in  a  porcelain  cruci- 
ble, or  on  a  piece  of  platinum  foil,  dried,  and  gently  ignited 
to  destroy  the  oxalic  acid.  The  residue  is  dissolved  in  hydro- 
chloric acid  and  the  solution  examined  according  to  6,  p.  161. 


163 


TABLE  IV.— SEPAKATION  OF  THE  THIRD  GROUP. 
In  the  Absence  of  Phosphoric  Acid  or  Oxalic  Acid. 

The  precipitate,  which  may  contain  Fe(0H)3,  A1(0H)3,  Cr(0H)3,  is 
treated  with  an  excess  of  sodium  hydroxide,  bromine  water  is  added,  and 
the  mixture  is  warmed  about  five  minutes  and  then  filtered. 


Insol.  Residue. 

Filtrate. 

Reddish-brown 

NagAlOg,  Na^CrO^. 

re(0H)3. 

Add  excess  of  ammonium   chloride  and  boil 

Dissolve  in  hydrochlo- 

until the  odor  of  ammonia  is  no  longer  per- 

ric  acid   and  dilute 

ceptible  and  then  filter. 

with  water,  add  po- 
tassium    ferrocj'^an- 

ide:  blue 

Precipitate. 

Filtrate. 

re,(Fe(CN)e)3 

White,  gelatinous 

Na^CrO,. 

indicates  presence  of 

A1(0H)3 

Acidulate     with     hy- 

iron. 

indicates  presence  of 

drochloric   acid  and 

aluminium. 

treat  with  an  excess 
of     hydrogen     sul- 
phide.     Warm  sev- 
eral    minutes,     and 
add  ammonium  hy- 
droxide   until    odor 
of  ammonia   is  per- 
ceptible, then  warm 
the  liquid  until  odor 
of  ammonia  is  barely 
perceptible.    Bluish- 
gray     or     greenish- 
gray 

Cr(0H)3 
indicates  presence  of 
chromium .    ( May  be 
confirmed  by  its  im- 
parting an   emerald 
color     to     a    borax 
bead.) 

164 


SEPARATION   OF  THE  FOURTH  GROUP. 

After  washing  the  precipitate  produced  by  ammonium  sul- 
phide (page  143),  while  on  the  filter,  with  water  containing 
hydrogen  sulphide,  the  filter  is  pierced  with  a  glass  rod  and 
the  precipitate  washed  with  cold  dilute  hydrochloric  acid  into 
a  beaker  placed  below.  Manganous  sulphide  and  zinc  sul- 
phide are  dissolved  by  the  dilute  hydrochloric  acid  as  man- 
ganous chloride  and  zinc  chloride,  while  nickelous  sulphide 
and  cobaltous  sulphide  remain  undissolved.  The  nickelous 
and  cobaltous  sulphides  are  collected  on  a  filter  and  w^ashed 
with  water  containing  hydrogen  sulphide. 

The  hydrochloric  acid  filtrate  is  warmed  until  the  hydrogen 
sulphide  is  completely  driven  off,  and  then  treated  with  sodium 
hydroxide  in  excess.  Manganese  is  precipitated  as  white 
manganous  hydroxide,  which,  when  exposed  to  the  air, 
rapidly  changes  to  brown  manganic  hydroxide ;  while  zinc, 
at  first  precipitated  as  zinc  hydroxide,  is  dissolved  as  Na2Zn02, 
sodium  zincate.  The  manganous  hydroxide  is  filtered  ofip, 
and  the  alkaline  filtrate  treated  with  hydrogen  sulphide, 
which  precipitates  zinc  as  white  zinc  sulphide. 

The  mixture  of  nickelous  sulphide  and  cobaltous  sulphide 
remaining  on  the  filter,  insoluble  in  hydrochloric  acid,  is  dis- 
solved by  heating  with  nitro-hydrochloric  acid.  The  greater 
part  of  the  excess  of  acid  is  driven  off  by  boiling,  and  the 
solution  neutralized  by  adding  sodium  hydroxide  drop  by 
drop  until  a  permanent  precipitate  of  hydroxides  is  formed. 
Acetic  acid  in  excess  and  sodium  acetate  are  then  added,  fol- 
lowed by  the  addition  of  an  excess  of  a  concentrated  solution 
of  potassium  nitrite.  If  cobalt  is  present,  a  yellow  crystal- 
line precipitate  of  potassium  cobaltic  nitrite  is  formed,  either 
immediately  or  after  standing  some  time.  After  several 
hours  the  precipitate  is  filtered  off,  and  the  filtrate  treated 


165 

with  sodium  hydroxide ;  the  formation  of  a  pale-apple-green 
precipitate  of  nickelous  hydroxide  indicates  the  presence  of 
nickel.  (The  precipitate  of  nickel  should  be  tested  in  a 
bead  of  borax  or  of  microcosmic  salt ;  see  8,  page  62.) 

TABLE  v.— SEPARATION  OF  THE  FOURTH  GROUP. 

The  precipitate,  which  may  contain  MnS,  ZnS,  NiS,  CoS,  is  treated 
with  cold  dilute  hydrochloric  acid  and  filtered : 


Insol.  Residue. 

Filtrate. 

NiS,  Cos. 

ZnCl^,  MnClj. 

Dissolve  in  nitro-hydrochloric  acid, 

Heat  to  drive  off  H„S,  add  ex- 
cess of  NaOH,  and  filter: 

evaporate  excess  of  acid,  neutral- 

ize  remainder  with   NaOH,  add 
HCoHoOo    in     excess     and     then 
NaC^HgO^andKNO^: 

Precipitate. 

Filtrate. 

White 

Na,ZnO,. 
Treat          with 
H,S: 

Precipitnte. 

Filtrate. 

Mn(OH)„ 
rapidly 

Yellow  crvstalline 

NiCl^. 

changing   to 

white 

K3Co(N0,)e 

Add  NaOH  : 

brown 

ZnS 

indicates    presence 

pale-apple- 

Mn(0H)3 

indicates   pres- 

of cobalt. 

green 

indicates   pres- 

ence of  zinc. 

Ni(0H)2 

ence  of  man- 

indicates  pres- 

ganese. 

ence            of 

nickel. 

SEPARATION   OF  THE  FIFTH  GROUP. 

The  members  of  the  Fifth  Group  may  be  separated  accord- 
ing to  the  following  method : 

A.  The  precipitate  produced  by  ammonium  carbonate 
(page  144),  consisting  of  carbonates,  is  dissolved,  while  on 
the  filter,  with  a  small  quantity  of  dilute  hydrochloric  acid, 
which  converts  the  carbonates  into  chlorides.  Only  a  small 
quantity  of  hydrochloric  acid  is  used,  so  that  the  solution 
may  be  concentrated  but  only  slightly  acid.  A  small  portion 
of  the  solution  of  chlorides  is  treated  with  a  concentrated 
solution  of  calcium  sulphate. 

(a)  If  upon  the  addition  of  the  calcium  sulphate  no  pre- 


166 

cipitate  is  formed,  either  immediately  or  after  standing  some 
time,  barium  and  strontium  are  absent.  The  remainder  of 
the  hydrochloric  acid  solution  (to  which  calcium  sulphate  has 
not  been  added)  is  treated  with  ammonium  hydroxide  and 
ammonium  oxalate,  when,  if  calcium  is  present,  a  white  pre- 
cipitate of  calcium  oxalate  is  formed. 

(6)  If  on  the  addition  of  calcium  sulphate  a  white  precipi- 
tate is  immediately  produced,  barium  is  probably  present ;  if 
a  turbidity  appear  after  some  time,  probably  strontium  only 
is  present.  In  either  case  the  remainder  of  the  hydrochloric 
acid  solution  (which  has  not  been  treated  with  calcium  sul- 
phate) is  evaporated  to  dryness  on  a  water-bath,  and  the 
residue  pulverized  and  extracted  with  strong  alcohol.  Barium 
chloride  remains  undissolved,  while  strontium  chloride  and 
calcium  chloride  enter  into  solution.  The  liquid  is  filtered 
through  a  dry^^^  filter,  and  a  portion  of  the  residue  on  the 
filter  is  placed  on  a  platinum  wire  and  held  in  the  Bunsen 
flame ;  a  green  color  imparted  to  the  flame  indicates  the  pres- 
ence of  barium.  The  alcoholic  filtrate  is  evaporated  on  a 
water-bath  to  ascertain  (by  a  residue  remaining)  whether 
anything  has  entered  into  solution.  Any  residue  (consisting 
of  chlorides)  remaining  is  evaporated  twice  to  dryness  with 
an  excess  of  concentrated  nitric  acid  (free  from  chlorine), 
which  converts  the  chlorides  into  nitrates  : 

SrCLj  +  2HNO3  =  Sr(N03)2  +  2HC1, 
and  the  residue  of  nitrates  is  then  extracted  with  strong  alco- 
hol as  before  described ;  calcium  nitrate  enters  into  solution, 
while  strontium  nitrate,  which  remains  undissolved,  is  col- 
lected on  a  filter,  and  a  portion  placed  on  a  platinum  wire  and 
held  in  the  Bunsen  flame ;  a  crimson  color  imparted  to  the 
flame  indicates  the  presence  of  strontium.     The  alcoholic  fil- 


1  A  filter  which  has  not  been  moistened  witii  water. 


167 

trate  is  now  evaporated  until  free  from  alcohol,  and  any  traces 
of  strontium  and  barium  are  precipitated  with  a  few  drops 
of  sulphuric  acid/^^  and  the  liquid  is  filtered  and  tested  for 
calcium  with  ammonium  hydroxide  and  ammonium  oxalate. 
The  formation  of  a  white  precipitate  indicates  the  presence 
of  calcium. 


TABLE  VI.— SEPAKATION  OF  THE  FIFTH  GROUP. 

The  precipitate,  which  may  contain  BaCOg,  SrCOg,  CaCOg,  is  dissolved 
in  a  small  quantity  of  HCl,  and  a  portion  of  the  solution  treated  with 
CaSO, : 


No    precipitate    is 
produced : 
Ba  and  Sr 

are  absent.  Treat 
the  remainder  of 
the  HCl  solution 
with       NH4OH 

and(NHJ.,CA: 
white     precipitate, 

CaCjO,, 
indicates    presence 

of  calcium. 


A  white  precipitate  is  produced. 
Evaporate  the  remainder  of  the  HCl  solution  to 
dryness  on  a  water-bath,  pulverize  the  residue, 
extract  with  strong  alcohol,  and  filter : 


Insol.  Residue. 

BaCl^. 

Place  a  portion 
on  platinum 
wire  and 
hold  in  the 
flame: 

a  green  color 
imparted  to 
the  flame  in- 
dicates pres- 
ence of  bar- 


Filtrate. 

SrCl^,  CaClj. 
Evaporate  to  dryness  on  a  water- 
bath,  evaporate  residue  twice 
to  dryness  with  cone.  HNO3, 
extract  the  residue  with  strong 
alcohol,  and  filter: 


Insol.  Residue. 

Sr(NOg),. 

Place  a  portion 
on  platinum 
wire  and 
hold  in  the 
flame: 

a  crimson  color 
imparted  to 
the  flame  in- 
dicates pres- 
ence of  stron- 
tium. 


Filtrate. 

Ca(N0g)2. 
Evaporate  un- 
til free  from 
alcohol,   add 
NH.OH  and 

(NlijAO^: 
white    precipi- 
tate, 
CaCjO^, 
indicates    pres- 
ence of   cal- 


*  From  concentrated  solutions  calcium  also  may  be  partly  precipitated, 
although,  because  of  its  solubility,  a  considerable  quantity  of  calcium  sul- 
phate remains  in  solution. 


168 


SEPARATION    OF    THE    SIXTH    GROUP. 

If  barium  and  calcium  were  found  in  the  Fifth  Group, 
traces  of  them  may  remain  in  the  filtrate  from  that  group, 
and  must  be  removed  before  proceeding  with  the  separation 
of  the  Sixth  Group.  For  this  purpose  a  few  drops  of  dilute 
sulphuric  acid  are  added  to  the  filtrate  to  precipitate  the 
barium,  and  ammonium  hydroxide  and  ammonium  oxalate 
added  to  precipitate  calcium.  If  precipitates  are  formed, 
they  are  removed  by  filtration.  A  portion  of  the  solution 
thus  rendered  free  from  barium  and  calcium,  or  the  filtrate 
from  the  Fifth  Group  which  originally  contained  no  barium 
or  calcium,  is  tested  for  magnesium  with  ammonium  chloride, 
ammonium  hydroxide,  and  sodium  hydrogen  phosphate.  If 
magnesium  is  present,  a  white,  crystalline  precipitate  of  am- 
monium magnesium  phosphate  will  appear,  either  immediately 
or  after  standing  some  time.  If  magnesium  is  not  present, 
the  remainder  of  the  solution  is  examined  according  to  I., 
page  1 68  ;  if  it  is  present,  the  solution  is  to  be  examined 
according  to  II.,  page  169. 

I.  The  remainder  of  the  solution  which  does  not  contain 
magnesium  is  placed  in  a  porcelain  crucible  or  dish  and 
evaporated  to  dryness  on  a  water-bath ;  it  is  then  gently 
heated  over  a  free  flame  until  vapors  of  ammonium  salts 
cease  to  be  evolved.  If  no  residue  remain,  potassium, 
sodium,  and  lithium  are  absent ;  if  a  residue  remain,  it  is 
tested,  by  means  of  the  flame-test,  for  lithium.  The  pro- 
duction of  a  carmine-colored  flame  indicates  the  presence  of 
lithium.  If  lithium  be  present,  the  residue  is  to  be  exam- 
ined according  to  III.,  page  170.  If  lithium  be  absent,  the 
remainder  is  then  dissolved  in  the  least  quantity  possible  of 
water,  and  the  concentrated  solution  divided  into  two  portions. 


169 

(a)  One  portion  is  placed  in  a  watch-glass,  treated  with 
platinic  chloride  and  a  small  quantity  of  alcohol,  and  stirred 
with  a  glass  rod.  If  potassium  is  present,  a  yellow  crys- 
talline precipitate  of  potassium  chlorplatinate  will  be  formed. 

(b)  The  second  portion  is  tested  for  sodium  by  adding  a 
clear,  freshly-prepared  solution  of  potassium  pyroantimonate. 
Sodium  salts  yield  with  potassium  pyroantimonate,  either  im- 
mediately or  after  standing  some  time,  a  white  crystalline  pre- 
cipitate of  sodium  pyroantimonate.  The  solution  to  be  tested 
for  sodium  must  not  be  acid  in  reaction,  or  flocculent  anti- 
monic  acid  will  be  precipitated.  If  acid  in  reaction,  the  solu- 
tion should  be  exactly  neutralized  with  ammonium  hydroxide 
before  making  the  test  with  potassium  pyroantimonate.^^^ 

II.  If  magnesium  is  present  in  the  solution,  it  must  be  re- 
moved before  the  tests  for  potassium,  sodium,  and  lithium  can 
be  made.  For  this  purpose  the  solution  containing  magnesium 
is  evaporated  to  dryness  on  a  water-bath,  and  the  residue 
gently  heated  over  a  free  flame  until  the  vapors  of  ammonium 
salts  cease  to  be  evolved.  The  residue  is  then  dissolved  in 
water  and  a  few  drops  of  hydrochloric  acid.  (The  presence 
of  ammonium  salts  interferes  with  the  precipitation  of  mag- 
nesium ;  see  1,  page  66.  The  residue  does  not  completely 
dissolve  in  water,  as  part  of  the  magnesium  salts  were  con- 
verted into  insoluble  basic  salts  by  the  heating.) 

The  solution   is  heated  to  the  boiling  point  and  barium 


^  To  detect  small  quantities  of  potassium,  sodium,  and  lithium,  ad- 
vantage may  be  taken  of  their  behavior  in  the  non-luminous  flame. 
Sodium  imparts  a  j'ellow  color,  potassium  a  violet  color,  lithium  a  oar- 
mine  color,  to  the  flame.  To  detect  the  potassium  flame  in  the  presence 
of  the  sodium  flame  (as  the  intense  yellow  .sodium  flame  obscures  the 
weaker  violet  potassium  flame),  a  piece  of  blue  glass  (cobalt  glass)  or  an 
indigo  prism  (which  absorbs  the  yellow  rays)  maybe  employed.  Viewed 
through  blue  glass  or  an  indigo  prism  the  potassium  flame  appears  crim- 
son-red in  color. 

H  15 


170 

hydroxide  added,  whereby  magnesium  hydroxide  is  precipi- 
tated : 

MgCl^  +  Ba(0H)2  =  Mg(OH)2  +  BaCl^. 
(Any  sulphuric  acid  which  might  be  present  would  also  be 
precipitated.)  The  magnesium  hydroxide  is  filtered  off,  and 
the  filtrate  treated  with  ammonium  carbonate  to  precipitate 
the  barium  of  the  barium  chloride  as  barium  carbonate.  The 
barium  carbonate  is  filtered  off,  the  filtrate  evaporated  to  dry- 
ness, and  the  residue  gently  heated  in  a  porcelain  dish  or 
crucible  until  vapors  of  ammonium  salts  cease  to  be  evolved 
and  the  residue  tested  by  the  flame  test  for  lithium.  If 
lithium  be  present,  the  residue  is  to  be  examined  according 
to  III.,  page  170.  If  lithium  be  absent,  the  residue  is  dis- 
solved in  a  small  quantity  of  water  and  the  solution  divided 
into  two  portions  and  tested  for  potassium  and  sodium,  as 
described  und(H'  a  and  b,  page  169. 

III.  If  lithium  has  been  detected  by  the  flame  test  in  the 
residue  mentioned  under  I.,  page  168,  or  II.,  page  169,  the 
residue  is  moistened  with  concentrated  hydrochloric  acid 
(which  converts  the  bases  into  chlorides),  and  evaporated  to 
dryness  on  a  water-bath.  The  residue  remaining  is  extracted 
with  a  mixture  consisting  of  equal  volumes  of  absolute  alco- 
hol and  ether.  Lithium  chloride  enters  into  solution,  leaving 
potassium  chloride  and  sodium  chloride  undissolved.  The 
liquid  is  filtered,  the  filtrate  evaporated  to  dryness  on  a 
water-bath,  and  a  portion  of  tlie  residue  placed  on  a  plati- 
num wire  and  held  in  the  non-luminous  flame.  If  lithium 
is  present,  a  carmine-red  color  will  be  imparted  to  the  flame. 

The  residue  insoluble  in  alcohol  and  ether  is  dissolved  in  a 
small  quantity  of  water  and  divided  into  two  portions.  One 
portion  is  placed  in  a  watch-glass,  platinic  chloride  and  a 
few  drops  of  alcohol  are  added,  and  the  liquid  is  stirred  with 
a  glass  rod.     If  potassium  is  present  a  yellow,  crystalline  pre- 


171 

cipitate  of  potassium  chlorplatinate  will  be  formed.  The 
other  portion  is  placed  in  a  watch-glass  and  treated  with  a 
clear,  freshly-prepared  solution  of  potassium  pyroantimonate 
and  the  liquid  stirred  with  a  glass  rod.  If  sodium  is  present 
a  white,  crystalline  precipitate  of  sodium  pyroantimonate  will 
be  formed. 


To  test  for  the  presence  of  ammonium  salts,  a  portion  of 
the  original  substance  or  solution  presented  for  analysis  is 
placed  in  a  test-tube,  treated  with  a  solution  of  sodium  hy- 
droxide, and  boiled.  If  ammonium  salts  are  present  ammo- 
niacal  gas  will  be  evolved,  which  may  be  recognized  by  its 
odor,  by  its  changing  turmeric  paper,  moistened  with  water, 
brown,  and  by  its  forming  white  clouds  of  ammonium  acetate 
when  a  glass  rod  moistened  with  acetic  acid  is  held  in  the 
atmosphere  containing  the  gas. 

In  using  turmeric  paper  in  this  test  care  must  be  taken  that 
the  turmeric  paper  does  not  come  in  contact  with  the  sides 
of  the  test-tube,  as  in  such  case  the  yellow  paper  may  be 
changed  to  brown  by  sodium  hydroxide  which  may  be  on 
the  glass.  Likewise  care  must  be  taken  that  in  the  ebul- 
lition of  the  liquid  none  of  it  is  projected  on  the  turmeric 
paper. 


172 


TABLE  Vila. -SEPARATION   OF  THE  SIXTH   GROUP. 


A.  Examination  for  Mg,  K,  Na,  Li. 

Test  the  filtrate  from  the  Fifth  Group  for  traces  of  Ba  with  H0SO4 
and  for  Ca  with  NH4OH  and  (NH4)2C204.  If  precipitates  are 
produced,  remove  them  by  filtration.  Test  a  portion  of  the 
solution  free  from  Ba  and  Ca  for  Mg  with  NH4CI,  NH4OH,  and 
NaaHPO*: 


A  precipitate  is  produced : 
MgNH4P04, 

indicating  presence  of  magne- 
sium. 

Evaporate  the  remainder  of  the 
solution  to  dryness  on  a 
water-bath,  gently  heat  resi- 
due over  a  free  flame  until 
vapors  of  ammonium  salts 
cease  to  be  evolved. 

Dissolve  residue  in  water  and  a 
few  drops  HCl,  boil,  add 
Ba(OH)2.  filter,  add  (NH4)2C03 
to  filtrate,  filter,  evaporate  fil- 
trate to  dryness  on  water- 
bath,  and  gently  heat  residue 
over  a  free  flame  until  vapors 
of  ammonium  salts  cease  to 
be  evolved. 

(Test  the  residue  for  lithium  by 
the  flame  test  (carmine).  If 
lithium  be  present,  proceed 
according  to  the  separation 
under  Table  VII6.) 


A  residue  remains : 
KCl,  NaCl. 

Dissolve  in  small 
quantity  of  water 
and  divide  into 
two  portions. 

To  one  portion  add 
PtCl4:  a  yellow, 
crystalline  pre- 
cipitate, 

K2PtCl6, 

I  indicates   presence 
'     of  pota.ssium. 
j  To   the  other  por- 
tion   add    clear, 
freshly  -  prepared 
solution  of  potas- 
sium      pyroanti- 
monate :  a  white, 
crystalline      pre- 
cipitate, 
Na^H2Sbj07, 
indicates    presence 
of  sodium. 


A  residue 
does  not 
remain : 
K  and  Na 
are       ab- 
sent. 


No  precipitate  is  produced. 

Evaporate  the  remainder  of  the 
solution  to  dryness  on  a  water- 
bath,  gently  heat  residue  over 
a  free  flame  until  vapors  of 
ammonium  salts  cease  to  be 
evolved. 

(Test  the  residue  for  lithium  by 
the  flame  test  (carmine).  If 
lithium  be  present,  proceed 
according  to  the  separation 
under  Table  VII6.) 


A  residue  remains : 
KCl,  NaCl. 

Dissolve  in  small 
quantity  of  water 
and  divide  into 
two  portions. 

To  one  portion  add 
PtCU:  'a  yellow, 
crystalline  pre- 
cipitate, 

K2PtCl6, 

indicates  presence 
of  potassium. 

To  the  other  por- 
tion add  clear, 
freshly-prepared 
solution  of  potas- 
sium pyroanti- 
monate :  a  white, 
crystalline  pre- 
cipitate, 
Na2H2Sb207, 

indicates  presence 
of  sodium. 


A  residue 
does  not 
remain : 
K  and  Na 
are       ab- 
sent. 


B.  Examina- 
tion for  Am- 
moniuni. 

Treat  the 
original 
substance 
or  solution 
with  NaOH 
and  boil : 
the  evolu- 
tion of  am- 
moniacal 
gas,  recog- 
nized by  its 
odor,  etc., 
indicates 
presence  of 
ammonium. 


173 


TABLE  yiI6.— SEPARATION  OF  THE  SIXTH  GROUP   (IN 
THE  PRESENCE   OF   LITHIUM). 

K,  Na,  Li. 

If  a  residue  remain  (see  Table  Vila.),  moisten  with  cone.  HCl,  evapo- 
rate to  dryness  on  a  water-bath,  extract  residue  with  a  mixture  of  absolute 
alcohol  and  ether,  and  filter : 


Insol.  Residue.                       < 

Filtrate. 

KCl,  NaCl. 

LiCl. 

Divide  into  two  portions. 

Evaporate  to  dryness  on  a  water-bath. 

To  one  portion  add  PtCl4 :  a  yellow  crys- 

Place a  portion  of  the  residue  on  a 

talline  precipitate, 

clean  platinum  wire  and  hold  in  the 

KaPtClo, 

non-luminous  flame :  a  carmine-red 

indicates  presence  of  potassium. 

color  imparted  to  the  flame  indicates 

To  the  other  portion  add  clear,  freshly- 

presence  of  lithium. 

prepared  solution  of  potassium  pvro- 

antimonate :  a  white,  crystalline  pre- 

cipitate, 

NasHaSbgOy, 

indicates  presence  of  sodium. 

15* 


VI.  EXAMINATION  FOR  ACIDS. 


The  examination  for  acids  should  always  be  preceded  by 
the  examination  for  bases  and  by  the  preliminary  examination. 
(See  pages  107,  108,  and  succeeding  pages.) 

The  number  of  acids  to  be  taken  into  consideration  depends 
upon  the  number  of  bases  present  and  upon  the  results  of  the 
preliminary  examination.  Acids  which  form  insoluble  com- 
pounds with  the  bases  found  in  the  solution  need  not  be 
sought  for ;  as,  for  example,  if  silver  is  found  in  the  solution, 
hydrochloric  acid  cannot  be  present,  or,  if  barium  is  found, 
it  is  useless  to  look  for  sulphuric  acid.  In  neutral  solutions 
containing  heavy  metals,  only  a  limited  number  of  acids  are 
to  be  considered,  as  most  of  the  salts  of  the  heavy  metals  are 
insoluble  in  water. 

In  solutions  having  an  acid  reaction  all  the  acids  are  to  be 
considered  which,  with  the  bases  present,  form  salts  soluble 
in  acid  solution.  (For  solubilities  see  Properties  of  the 
Acids,  page  73  and  succeeding  pages,  and  also  table  on 
page  180.) 

If  heavy  metals  (metals  of  the  First,  Second,  Third,  Fourth, 
and  Fifth  Groups)  are  present,  they  must,  in  many  cases,  be 

174 


175 

removed  before  proceeding  with  the  tests  for  acids.  When 
possible,  this  is  accomplished  by  the  addition  of  an  excess  of 
sodium  carbonate  to  the  solution  and  boiling,  thereby  pre- 
cipitating the  metals  as  carbonates  or  oxides.  The  precipi- 
tate is  filtered  off,  and  the  filtrate  is  divided  into  two  unequal 
portions.  The  larger  portion  is  neutralized  with  nitric  acid 
and  examined  according  to  A,  page  176,  and  the  smaller 
portion  is  acidulated  with  sulphuric  acid  and  used  in  test- 
ing for  nitric  and  acetic  acids.  It  is  advisable  to  gently  heat 
the  solution  after  acidulation,  in  order  to  completely  expel 
carbon  dioxide.^^^  Stannic  oxide  and  arsenic  are  removed  by 
precipitating  with  hydrogen  sulphide.  In  this  operation  sul- 
phuric acid  may  result  from  the  oxidation  of  the  hydrogen 
sulphide.  In  such  cases  the  original  solution  should  be  test-ed 
directly  for  sulphuric  acid  and  hydrochloric  acid. 

In  the  examination  of  solutions  having  an  alkaline  reaction, 
they  should  be  neutralized  with  nitric  acid  or  sulphuric  acid 
before  beginning  the  examination  for  acids.  In  case  a  pre- 
cipitate is  produced  the  acid  should  be  added  in  excess,  the 
precipitate  filtered  off,  and  the  filtrate  neutralized  with  an 
alkali.     (See  page  122,  b.) 

Salts  which  are  insoluble  in  water  are  examined  for  acids 
by  treating  them  directly  (without  first  dissolving  them)  with 
a  solution  of  sodium  carbonate.  When  heated  to  boiling  the 
acid  enters  into  solution  as  a  sodium  salt,  while  the  base 
remains  as  an  insoluble  oxide  or  carbonate.  The  liquid  is 
filtered,  and  the  filtrate  containing  the  sodium  salts  is  neu- 
tralized with  nitric  acid  or  acetic  acid  as  above  described. 

1  If  the  carbon  dioxide  has  not  been  completely  expelled,  precipitates 
of  carbonates  may  be  produced  on  the  addition  of  the  three  group  re- 
agents ;  with  barium  chloride  soluble  barium  bicarbonate  might  be  formed, 
which  would  appear  as  a  precipitate  only  after  boiling. 


176 

In  examining  for  acids  when  fusion  is  necessary,  see  the 
chapter  on  Sohition  and  Fusion,  page  1 20. 


A.  Separate  portions  of  the  sohition  neutralized  with  nitric 
acid  are  first  examined  regarding  their  behavior  with  the 
three  group  reagents :  one  portion  is  treated  with  BaCla,  a 
second  with  Pb( €211302)2,  and  a  third  portion  with  AgNOg. 
The  acids ^^^  which  produce  precipitates  with  the  group  re- 
agents and  the  properties  of  the  precipitates  are  given  in  the 
following  table  (page  178)c,  In  many  cases  reasonably  cer- 
tain conclusions  as  to  which  acids  are  present  may  be  drawn 
from  the  color  of  the  precipitates  and  from  the  behavior  of 
the  latter  with  the  difterent  solvents,  if  at  the  same  time  it  is 
considered  which  acids  could  possibly  be  present  under  the 
existing  conditions;  for  example,  if  a  precipitate  soluble  in 
nitric  acid  is  produced  by  argentic  nitrate,  the  presence  of 
hydrochloric  acid,  hydrobromic  acid,  etc.,  is  excluded.  If 
the  precipitate  produced  by  barium  chloride  is  insoluble  in 
acids,  sulphuric  acid  or  hydrofluosilicic  acid  must  be  present. 
After  having  ascertained  to  which  group  or  groups  the  acids 
belong,  and  obtaining  reasonable  information,  by  the  solu- 
bility and  color  of  the  precipitate  produced  by  the  group 
reagents  for  acids,  of  the  particular  acids  present,  their  pres- 
ence is  to  be  confirmed  by  applying  to  the  solution  neutral- 
ized with  nitric  acid  the  special  characteristic  tests  for  acids 
given  in  the  pages  beginning  with  page  182. 


'  For  a  classification  of  the  acids  composing  the  four  groups,  see  page 
178  :  in  this  classification  oxalic  acid  and  tartaric  acid  belong  to  the  second 
group,  and  acetic  acid  to  the  fourth  group. 


177 

NitHc  acid,  chloric  acid,  and  acetic  acid  are  not  precipi- 
tated by  the  three  group  reagents ;  therefore,  special  tests 
characteristic  of  these  acids  must  be  made.  Eor  the  tests  for 
nitric  acid,  see  page  189  ;  chloric  acid,  page  190 ;  acetic  acid, 
page  190. 


178 


TABLE  VIII— BEHAVIOR  OF  THE   ACIDS 


Pbecipitate  in  the  presence  of 


On  the  Addition  of  BaCl2. 


Group  I. 


(  Sulphu7'ic  acid 


Qroup  II. 


Hydrojluosilicic  acid: 
Sulphurous  acid:  .  . 
Hyposulphurous  acid: 


Phosphoric  acid: 
Boric  acid:      .    . 


Hydrofiuoric  acid. 
Carbonic  acid:    . 


Silicic  acid: 
Arsenious  acid: 
Arsenic  acid : 
Chromic  acid: 
Oxalic  acid:    . 
[  Tartaric  acid: 


QronpIII.  - 


Hydrochloric  acid : 
Hydrobroniic  acid: 
Hydriodic  acid : 
Hydrocyanic  acid: 


Hydrqferrocyanic  acid . 
Hydroferricyanic  acid: 
Sulphydric  acid:    .    . 


Nitrous  acid :  .  . 
Hypochlorous  acid , 
Sulphocyanic  acid: 


{Nitric  acid: 
Chloi'ic  acid . 
Acetic  acid: 


white  (insoluble  in  HCl)    .... 
white  (insoluble  in  HCl)    .... 

white  (soluble  in  HCl :  with  evo- 
lution of  SO2) 

white  (soluble  in  large  quant,  of 
water  ;  soluble  in  "HCl :  with 
evolution  of  SO,  and  separation 
of  S) 

white  (soluble  in  HCl) 

white  (precipitated  only  in  cone, 
solutions  ;  soluble  in  HCl) 

white  (soluble  in  HCl) 

white  (soluble  in  HCl :  with  effer- 
vescence) 

white  (soluble  in  HCl) 

white  (soluble  in  HCl) 

white  (soluble  in  HCl ) 

yellow  (soluble  in  HCl)      .... 

white  (soluble  in  HCl) 

white  (soluble  in  HCl) 


179 


WITH  THE   GKOUP   REAGENTS. 


On  the  Addition  of  Pb(C2H802)j. 


On  the  Addition  of  AgNOa. 


white  (slightly  soluble  in  HNO3)  • 


white  (soluble  in  HNO3)     .    .    .    . 

white    (soluble    in    HNO3;    with 
separation  of  S) 


^  white  (soluble  in  HNO3)     .    . 

white    (soluble    in    excess   of 

agent ;  soluble  in  HNO3) 


with 


white  (soluble  in  HNO3) 
white    (soluble    in    HNO, 

effervescence) 
white  (soluble  in  HNO3) 
white  (soluble  in  HNO3) 
white  (soluble  in  HNO3) 
yellow  (soluble  in  HNO3) 
white  fsoluble  in  HNO3) 
white  (soluble  in  HNO3) 


white   (crystalline,  soluble  in  hot 

water) 
white  (soluble  with  great  difficulty 

in  water) 
yellow  (crystalline,  soluble  in  hot 

water) 
white  (insoluble  in  water ;  soluble 

in  HNO3) 
white  (insoluble  in  HNO3)      .    .    . 


white  (soluble  in  HNO3;   becomes 

gray  on  boiling) 
white   (soluble   in   HNO3;    rapidly 

becomes  black) 


yellowish  white  (soluble  in  HNO3) 
white  ^precipitated  only  from  cone, 
solutions ;  soluble  in  HNO3 ;  de- 
composed by  water) 


black  (soluble  in  HNO3  ^^^  warm- 
ing) 
yellow  coloration       


white  (becomes  brown,  due  to  sep- 
aration of  PbOj) 


white  (soluble  in  HNO3 ;  on  boiling 
becomes  yellow  or  brown) 

yellow  (soluble  in  HNO3) 

yellow  (soluble  in  HNO,) 

reddish  brown  (soluble  in  HNO3) 

purplish  red  (soluble  in  HNO3) 

white  (soluble  in  HNO3) 

white  (soluble  in  HNO3 ;  separation 
of  Ag  on  boiling) 

white  (curdy,  insoluble  in  HNO3) 

yellowish  white  (insoluble  in  HNO3) 

yellowish  white  (insoluble  in  HNO3) 

white  (curdy,  insoluble  in  HNOj) 

white  (insoluble  in  HNO,) 
I  yellowish  white  (insoluble  in  HNO3) 

black  (soluble  in  HNO3  on  warm- 
ing) 

white  (soluble  in  large  quant,  of 
water) 

white  (=AgCl) 

white  (curdy,  insoluble  in  dil.  HNO3) 


180 


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182 

TESTS    FOR    ACIDS. 

Sulphuric  Acid.     (Sulphates.) 

Sulphates  when  fused  (as  in  the  preliminary  examination) 
with  sodium  carbonate  on  charcoal  and  a  portion  of  the  fused 
mass  is  placed  on  a  silver  coin  and  moistened  with  water  pro- 
duce a  brownish  or  black  stain  on  the  coin. 

Barium  chloride  produces  a  white  precipitate  of  barium 
sulphate,  insoluble  in  acids. 

Plumbic  acetate  produces  a  white  precipitate  of  plumbic 
sulphate,  soluble  in  neutral  ammonium  tartrate. 

Tests  for  sulphuric  acid  should  never  be  made  in  solutions 
which  have  been  treated  with  hydrogen  sulphide,  because  of 
the  probability  of  the  presence  of  sulphuric  acid  resulting 
from  the  oxidation  of  hydrogen  sulphide. 

Tests  for  sulphuric  acid  can  be  made  in  acid  solutions  con- 
taining bases. 

Hydrofluosilicic  Acid,     {Silicofluorides.) 

Hydrofluosilicic  acid  is  not  precipitated  by  plumbic  acetate, 
but  is  j^recipitated  by  potassium  nitrate  as  gelatinous  potas- 
sium silicofluoride  (see  3,  page  74). 

Sulphurous  Add.     (Sulphites.) 

Sulphites  when  fused  with  sodium  carbonate  on  charcoal 
and  a  portion  of  the  fused  mass  is  placed  on  a  silver  coin  and 
moistened  with  water  produce  a  brownish  or  black  stain  on 
the  coin. 

On  acidulating  a  solution  of  a  sulphite  with  hydrochloric 
acid,  sulphurous  anhydride  is  evolved,  which  may  be  recog- 
nized by  its  odor  of  burning  sulphur  and  by  its  action  upon 
moistened  potassium  iodate  starch-paste  paper,  the  latter  be- 
coming blue,  owing  to  the  iodine  separated  by  the  sulphurous 
anhydride  from  the  iodate  acting  upon  the  starch. 


183 

Argentic  nitrate  precipitates  white  argentic  sulphite,  soluble 
in  nitric  acid.  On  boiling  the  precipitate  with  water,  it  is 
decomposed,  with  the  separation  of  finely-divided,  gray  metal- 
lic silver. 

To  detect  sulphurous  acid  in  the  presence  of  hyposulphur- 
ous  acid,  see  6,  page  76. 

Hyposulphurous  Acid.     (Hyposulphites,) 

Hyposulphites  when  fused  with  sodium  carbonate  on  char- 
coal and  a  portion  of  the  fused  mass  is  placed  on  a  silver 
coin  and  moistened  with  water  produce  a  brownish  or  black 
stain  on  the  coin. 

Hydrochloric  acid  or  sulphuric  acid  added  to  a  hyposul- 
phite causes  the  evolution  of  sulphurous  anhydride  (odor  of 
burning  sulphur)  and  a  milkiness  due  to  the  separation  of 
sulphur. 

Argentic  nitrate  produces  a  white  precipitate  of  argentic 
hyposulphite,  which  rapidly  changes  to  brown  and  finally  to 
black  argentic  sulphide.  As  argentic  hyposulphite  is  soluble 
in  an  excess  of  a  hyposulphite  of  an  alkali,  precipitation 
occurs  only  when  an  excess  of  the  argentic  nitrate  is  added. 

To  detect  sulphuric  acid  and  other  acids  in  the  presence  of 
hyposulphurous  acid,  the  latter  acid  must  be  decomposed  by 
gently  warming  with  hydrochloric  acid,  the  liquid  filtered, 
and  the  tests  for  sulphuric  acid  and  acids  other  than  hydro- 
chloric acid  made  in  the  filtrate. 

.Phosphoric  Acid.     (Phosphates.) 

Ammonium  chloride,  ammonium  hydroxide,  and  mag- 
nesium sulphate  (magnesia  mixture),  added  in  turn  to  a  solu- 
tion of  a  phosphate,  produce  a  white,  crystalline  precipitate 
of  ammonium  magnesium  phosphate. 

Ammonium   molvbdate,  added  in  excess  with  a  consider- 


184 

able  quantity  of  nitric  acid,  produces  a  yellow  precipitate  of 
ammonium  phosphomolybdate. 

(If  arsenic  acid  is  present,  it  must  be  completely  removed 
by  precipitation  with  hydrogen  sulphide  before  testing  for 
phosphoric  acid.  With  reference  to  the  behavior  of  silicic 
acid  with  ammonium  molybdate,  see  3,  page  85.) 

Bo)ic  Acid,     (Borates.) 

Turmeric  paper  dipped  in  an  aqueous  solution  of  boric 
acid,  or  of  a  borate  acidified  with  hydrochloric  acid,  and 
warmed  until  dry,  becomes  reddish  brown  in  color. 

Boric  acid  alone,  or  borates  placed  in  a  dish  and  moistened 
with  a  few  drops  of  concentrated  sulphuric  acid,  covered  with 
alcohol,  and  the  latter  ignited,  impart  a  greenish  color  to  the 
flame.  (Other  substances,  as  copper,  which  might  also  im- 
part a  green  color  to  the  flame  should  be  removed  before 
making  the  test.) 

Hydrofluoric  Acid.     (Fluorides.) 
Etches  glass  (see  4,  page  82). 

Carbonic  Add.     (Carbonates.) 

On  adding  an  acid  to  a  carbonate,  effervescence  occurs,  due 
to  the  evolution  of  carbon  dioxide.  The  presence  of  carbon 
dioxide  is  confirmed  by  the  production  of  a  white  turbidity 
or  precipitate,  due  to  the  formation  of  calcium  carbonate  with 
clear  calcium  hydroxide  solution  (see  2,  page  83). 

Silicic  Acid.     (Silicates.) 

A  portion  fused  in  a  bead  of  microcosmic  salt  yields  a  bead 
in  which  the  silica  is  not  dissolved,  but  swims  in  the  fused 
bead  as  small  opaque  particles  (see  4,  page  85). 

Arsenious  Add.     (Arsenites.) 
Arsenic  Add.     (Arseniates.) 


185 

Chromic  Add.     (Chromates.) 

These  will  have  been  detected  in  the  preliminary  exam- 
ination and  in  the  examination  for  bases. 

Argentic  nitrate  added  to  a  solution  of  arsenious  acid,  fol- 
lowed by  the  addition  of  ammonium  hydroxide,  drop  by 
drop,  or  to  a  solution  of  an  arsenite,  produces  a  yellow, 
curdy  precipitate  of  argentic  arsenite,  soluble  in  ammonium 
hydroxide  and  in  nitric  acid. 

Argentic  nitrate  added  to  a  solution  of  arsenic  acid,  fol- 
lowed by  the  addition  of  ammonium  hydroxide,  drop  by 
drop,  or  to  a  solution  of  an  arseniate,  produces  a  reddish- 
brown  precipitate  of  argentic  arseniate,  soluble  in  ammonium 
hydroxide  and  in  nitric  acid. 

Arsenious  acid  may  be  detected  in  the  presence  of  arsenic 
acid  by  its  being  immediately  precipitated  as  arsenious  sul- 
phide by  hydrogen  sulphide,  whereas  arsenic  axjid  is  pre- 
cipitated only  after  continuing  the  introduction  of  hydrogen 
sulphide  for  some  time. 

Arsenic  acid  is  detected  in  the  presence  of  arsenious  acid 
by  the  formation  of  a  white,  crystalline  precipitate  of  am- 
monium magnesium  arseniate  on  the  addition  of  magnesia 
mixture  (see  8,  page  35).  Arsenious  acid  does  not  produce  a 
precipitate  with  magnesia  mixture. 

Chromic  acid  produces  a  yellow  precipitate  with  plumbic 
acetate  and  a  purplish-red  precipitate  with  argentic  nitmte 
(see  3,  page  86,  and  4,  page  86). 

Oxalic  Acid.     (Oxalates.) 

Tartaric  Acid.     (Tarirates.) 

Produce  white  precipitates  with  calcium  chloride.  They 
may  be  distinguished  when  together  by  the  behavior  of  their 
calcium  salts :  calcium  oxalate  is  insoluble  and  calcium  tar- 
trate soluble  in  acetic  acid. 

16* 


186 

Hydrochlonc  Acid.     (Chlorides.) 

Hydrobromic  Acid.     {Bromides.) 

Hydriodic  Acid.     (Iodides.) 

Hydrocyanic  Acid.     (Cyanides.) 

All  are  precipitated  by  argentic  nitrate  respectively  as 
chloride,  bromide,  iodide,  and  cyanide  of  silver,  and  are  dis- 
tinguished by  the  behavior  of  their  silver  salt  with  ammonium 
hydroxide.  Argentic  chloride  and  argentic  cyanide  are  easily 
soluble  in  dilute  ammonium  hydroxide.  Argentic  bromide 
is  soluble  in  concentrated  ammonium  hydroxide ;  argentic 
iodide  is  insoluble  in  ammonium  hydroxide. 

If  the  precipitate  produced  on  the  addition  of  argentic 
nitrate  is  insoluble  in  nitric  acid  but  soluble  in  ammonium 
hydroxide,  hydriodic  acid  is  absent,  but  hydrochloric  acid, 
hydrocyanic  acid,  and  hydrobromic  acid  may  be  present.  A 
test  for  hydrocyanic  acid  may  be  made  by  means  of  the 
Prussian-blue  reaction  (see  4,  page  94),  and  for  hydrobromic 
acid  with  chlorine- water  and  chloroform  or  carbon  disulphide 
(see  5,  page  91). 

If  neither  hydrobromic  acid  nor  hydrocyanic  acid  is  present, 
the  solubility  of  the  silver  precipitate  in  ammonium  hydrox- 
ide proves  the  presence  of  hydrochloric  acid.  If  hydrobromic 
acid  or  hydrocyanic  acid  is  present,  the  distillation  test  with 
potassium  dichromate  and  sulphuric  acid  must  be  made  for 
hydrochloric  acid  (see  4,  page  89). 

If  the  precipitate  is  insoluble  or  only  partly  soluble  in 
ammonium  hydroxide,  the  presence  or  absence  of  hydriodic 
acid  must  be  established  by  means  of  chlorine-water  and 
chloroform  or  carbon  disulphide  (see  6,  page  92).  If  a  pink- 
ish-violet color  is  produced,  chlorine- water  is  added  drop  by 
drop  until  either  decolorization  occurs  (absence  of  hydrobro- 
mic acid)  or  the  yellow  color,  due  to  the  presence  of  bromine 


187 

(which  was  obscured  by  the  pinkish-violet  color  produced  by 
iodine),  appears  (see  5,  page  91). 

The  test  for  hydrocyanic  acid  should  be  made  as  before 
described  (4,  page  94).  The  distillation  test  for  the  detection 
of  hydrochloric  acid  is  to  be  employed  when,  in  addition  to 
hydriodic  acid,  hydrobromic  acid  or  hydrocyanic  acid  is 
present.  If  hydrobromic  acid  or  hydrocyanic  acid  is  ab- 
sent, hydrochloric  acid  may  be  detected  in  the  presence  of 
hydriodic  acid  by  the  solubility  of  the  silver  precipitate  in 
ammonium  hydroxide. 

It  should  be  remembered  that  chloride,  bromide,  iodide, 
and  cyanide  of  silver  are  soluble  in  hyposulphites  of  the 
alkalies ;  therefore  in  the  presence  of  hyposulphites  the  hypo- 
sulphurous  acid  should  be  removed  by  gently  warming  with 
nitric  acid. 

As  argentic  nitrate  fails  to  produce  a  precipitate  in  solu- 
tions of  mercuric  cyanide,  the  presence  of  mercuric  cyanide 
must  be  proved  according  to  4,  page  128. 

Hydrqferrocyanic  Acid.     (Ferrocyanides.) 

Ferric  chloride  produces  a  dark-blue  precipitate  of  ferric 
ferrocyanide  (Prussian  blue),  insoluble  in  acids  (see  5,  page  95). 

Cupric  sulphate  produces  a  precipitate  of  brownish-red 
cupric  ferrocyanide. 

Hydroferricyanic  Acid.     {Ferrieyanides.) 

Ferrous  sulphate  precipitates  blue  ferrous  ferricyanide 
(TurnbulFs  blue),  insoluble  in  acids. 

Ferric  chloride  fails  to  produce  a  precipitate,  but  produces 
a  dark  coloration  in  the  liquid,  due  probably  to  the  produc- 
tion of  ferric  ferricyanide  (see  3,  page  96). 

Cupric  sulphate  precipitates  greenish-yellow  cupric  ferri- 
cyanide. 


188 

Sulphocyanic  Acid.     (Sidphocyanides,) 

Argentic  nitrate  precipitates  white,  curdy  argentic  sulpho- 
eyanide,  insoluble  in  water  and  in  dilute  nitric  acid. 

Ferric  chloride  produces  an  intense  claret-red  coloration, 
due  to  the  formation  of  soluble  ferric  sulphocyanide.  The 
coloration  in  dilute  solutions  is  pale  red.  Mercuric  chloride 
destroys  the  coloration. 

Hydriodic  add  (iodides),  hydrobromic  add  (bromides),  and 
hydrochloric  acid  (chlorides)  are  detected  in  the  presence  of 
hydroferrocyanic  acid  and  hydroferricyanic  acid  by  means  of 
chlorine-water  and  chloroform,  and  by  distillation  with  potas- 
sium bichromate  and  sulphuric  acid. 

To  detect  hydrocyanic  acid  in  the  presence  of  hydroferro- 
cyanic acid  and  hydroferricyanic  acid,  the  solution  is  acidu- 
lated with  hydrochloric  acid,  and  calcium  carbonate  is  imme- 
diately added  until  carbon  dioxide  ceases  to  be  evolved.  A 
test  for  hydrocyanic  acid  is  then  made  by  the  ammonium 
sulphocyanide  reaction  (see  5,  page  94).  The  hydrochloric 
acid  liberates  hydrocyanic  acid  as  well  as  hydroferrocyanic 
acid  and  hydroferricyanic  acid,  but  only  the  two  latter  pos- 
sess the  property  of  decomposing  carbonates  to  form  salts; 
hydrocyanic  acid,  therefore,  remains  in  the  free  state. 

Hydrogen  Sulphide.     (Sulphides.) 

The  presence  of  sulphides  is  detected  when  making  the 
preliminary  examination. 

A  soluble  sulphide  placed  on  a  clean  silver  coin  and 
moistened  with  a  few  drops  of  water  produces  a  brownish  or 
black  stain  on  the  coin. 

Nitric  acid  or  nitro-hydfochloric  acid  decomposes  sulphides, 
with  the  separation  of  sulphur ;  hydrochloric  acid  causes  the 
evolution  of  hydrogen  sulphide  if  it  should  have  any  action 
at  all. 


189 

Plumbic  acetate  produces  in  solutions  of  sulphides  a  black 
precipitate  of  plumbic  sulphide. 

Sodium  nitro-prusside  solutions  are  colored  violet  by  sul- 
phides, but  not  by  free  hydrogen  sulphide. 

Nitrous  Acid.     (Nitrites.) 

On  the  addition  of  an  acid  to  a  nitrite,  brownish-red  fumes 
of  nitrogen  dioxide  are  evolved. 

On  adding  a  few  drops  of  sulphuric  acid  to  a  solution  of 
a  nitrite,  cooling  the  liquid,  and  adding  ferrous  sulphate,  a 
brown  or  black  coloration  is  produced  (see  5,  page  99). 

Potassium  iodide  (or  cadmium  iodide),  starch  paste,  and  a 
few  drops  of  dilute  sulphuric  acid  added  to  a  solution  of  a 
nitrite  produce  a  blue  coloration  (see  6,  page  100). 

Before  testing  for  nitric  acid  in  the  presence  of  nitrous  acid, 
the  nitrous  acid  must  be  decomposed  by  being  boiled  a  suffi- 
cient length  of  time  with  a  solution  of  ammonium  chloride : 
KNO2  +  NH4CI  =  KCl  +  N2  +  2H2O. 

Hypoehlorous  Acid.     (^Hypochlorites.) 

Hydrochloric  acid  decomposes  hypochlorites,  with  the  evo- 
lution of  chlorine. 

Plumbic  acetate  produces  in  solutions  of  hypochlorites  at 
first  a  white  precipitate  of  plumbic  chloride,  which  soon 
becomes  yellow  and  finally  brown,  due  to  the  formation  of 
lead  dioxide  (see  3,  page  100). 

Nitric  Acid.     (Nitrates.) 

On  adding  a  small  quantity  of  concentrated  sulphuric  acid 
to  a  solution  of  a  nitrate,  cooling,  and  placing  a  crystal  of 
ferrous  sulphate  in  the  liquid,  a  brownish  or  black  ring  is 
formed  around  the  crystal  (see  3,  page  101). 

With  potassium  iodide  (or  cadmium  iodide),  starch  paste, 


190 

and  dilute  sulphuric  acid  nitrates  do  not  produce  a  blue 
discoloration  unless  a  fragment  of  metallic  zinc  is  added. 
(Distinction  from  nitrites.     See  4,  page  101.) 

Before  testing  for  nitric  acid  in  the  presence  of  hydriodic 
acid  or  hydrobromic  acid,  the  two  latter  acids  must  be  re- 
moved by  precipitation  with  argentic  sulphate  or  with  plumbic 
acetate,  the  precipitate  filtered  off,  and  the  tests  for  nitric  acid 
made  in  the  filtrate. 

Chloric  Acid.     (Chlorates.) 

On  warming  a  solution  of  a  chlorate  with  hydrochloric 
acid  the  liquid  becomes  greenish  yellow  in  color,  and  greenish- 
yellow  fumes  of  a  mixture  of  chlorine  and  chlorine  tetroxide 
are  evolved. 

Concentrated  sulphuric  acid  poured  upon  a  very  small 
portion  of  a  solid  chlorate  causes  the  evolution  of  chlorine 
tetroxide  (see  4,  page  103). 

Chlorates  in  the  solid  state  on  being  strongly  heated  are 
converted  into  chlorides.  On  dissolving  the  residue  in  water 
and  testing  for  a  chloride  with  argentic  nitrate,  a  white  pre- 
cipitate of  argentic  chloride  will  be  produced.  (A  chlorate 
itself,  free  from  chlorides,  does  not  yield  a  precipitate  with 
argentic  nitrate.) 

Acetic  Acid.     (Acetates.) 

On  adding  ferric  chloride  to  a  solution  of  an  acetate  and 
boiling  the  liquid,  a  brownish-red  precipitate  of  basic  ferric 
acetate  is  formed. 

Sulphuric  acid  added  to  an  acetate  and  the  liquid  warmed 
liberates  acetic  acid,  Avhich  is  recognized  by  its  odor  of  vinegar. 

Alcohol  added  to  a  cooled  solution  of  an  acetate  containing 
free  sulphuric  acid  and  then  warmed  produces  acetic  ether, 
which  is  recognized  by  its  apple-like  odor  (see  6,  page  104). 


APPENDIX. 


BEHAVIOR  OF   THE   COMPOUNDS   OF  THE   RARE 
ELEMENTS. 


The  deportment  of  the  rare  elements  and  their  compounds 
when  subjected  to  the  usual  preliminary  examination,  as  well 
as  the  behavior  of  these  elements  with  the  ordinary  group 
reagents,  will  be  treated  of  in  the  following  pages.  It  is  not 
intended  to  give  a  detailed  description  of  the  separation  of 
the  rare  elements  from  one  another  or  from  the  more  fre- 
quently occurring  elements,  but  in  the  latter  part  of  the 
appendix  a  few  examples  are  given  of  the  separation  of  the 
rare  elements  in  minerals  which  may  be  easily  procured. 


I.    BEHAVIOR    IN   THE    PRELIMINARY    EXAMINA- 
TION. 

(a)  On  heating  the  substance  in  a  glass  reduction-tube : 

Titanic  acid  becomes  yellow  to  brown. 

Niohie  acid  becomes  yellow. 

TantaUc  acid  becomes  pale  yellow. 

Selenium  and  selenides  yield  a  reddish-brown  sublimate : 
a  portion  heated  in  a  tube  open  at  both  ends  and  held 
obliquelv  in  the  flame  gives  a  radish-like  odor. 

191 


192 

Tellurium  sublimes ;  heated  in  a  tube  open  at  both  ends, 
it  burns,  producing  dense  white  clouds. 

(6)  On  heating  the  substance  with  the  blowpipe  flame  on 
charcoal,  there  are  produced  : 
Pused  metallic  globules : 

Gold :  yellow,  ductile,  without  incrustation. 

Thallium:  white,  ductile,  yellow  incrustation. 

Indium, :  white,  ductile,  white  incrustation. 
Incrustation,  without  metallic  globule  : 

Tellurium. 
Infusible  metallic  masses : 

Tungsten, 

Molybdenum^ 

Platinum^ 

Palladium,  etc. 
White  masses 
(When  heated  with  cobaltous  nitrate  solution)  : 

Titanie  acid  becomes  yellowish  green. 

Niobic  acid  becomes  dirty  green. 

TantaUc  acid  becomes  flesh  color. 

Beryllia  becomes  gray. 
Brownish-red  masses : 

Selenixim  compounds. 

Tellurium  compounds. 

When  placed  on  a  silver  coin  and  moistened  with  water, 
a  brown  or  black  stain  is  produced  on  the  coin. 
When  treated  with  hydrochloric  acid,  hydrogen  sele- 
nide  and  hydrogen  telluride  are  evolved. 

(c)  On  fusing  tl>e  substance  in  a  bead  of  microcosmic  salt 
the  following  colored  beads  result  in  the 


Reducing  Flame, 
Green. 


Colorless. 


193 

Oxidizing  Flame. 
Uranium :  yellow  when  hot, 

yellowish  green  when 
cold. 
Cerium:    reddish    yellow    when 
hot, 
lighter  reddish  yellow 
to     colorless     when 
cold. 
Didymium :  colorless. 

Titanium :  colorless. 
Niobium :  colorless. 
Tungsten:  colorless. 
Molybdenum :  colorless. 
Vanadium :  colorless. 

Gold  and  platinum  are  not  dissolved  in  the  bead  of  micro- 
cosmic  salt. 


Amethyst  changing 

to  violet. 
Violet. 

Blue  or  violet. 
Blue. 
Black. 
Green. 


0-2 


3 


(d)  Examination  in  the  flame. 
The  non-luminous  flame  is  colored  by 
Lithium :  carmine-red. 
Rubidium:  violet. 
Gcesium:  violet. 
Indium:  bluish  violet. 
Selenium:  ultramarine-blue. 
Tellurium :  blue  bordered  with  green. 
Thallium:  intense  green. 
Molybdic  acid:  yellowish  green. 
Lithium,  rubidium,  ccesium,  indium,  thallium,  and  gallium 
are  best  detected  by  means  of  the  spectroscope.     Erbium  and 
didymium  also  furnish  absorption  spectra. 

I        n  17 


194 


II.  BEHAVIOR  WITH   THE  GROUP   REAGENTS. 
FIRST  GROUP. 

Hydrochloric  acid  precipitates : 

Thallium :  as  white  curdy  TlCl,  thallous  chloride,  solu- 
ble with  difficulty  in  water. 
From  alkaline  solutions : 

Molyhdic  axnd :  as  white  H2M0O4,  molybdic  acid,  soluble 
in  an  excess  of  hydrochloric  acid. 

Tungdic  acid :  as  white  H2WO4,  tungstic  acid,  insoluble 
in  an  excess  of  hydrochloric  acid ;  becomes  yellow  on 
boiling. 

Tantalic  add :  as  white  HTaOg,  tantalic  acid,  soluble  in 
an  excess  of  hydrochloric  acid,  producing  opalescence 
in  the  liquid. 

SECOND  GROUP. 

Hydrogen  sulphide  precipitates : 


ii 

B  5 


BS 


Palladium :  as  black  PdS,  palladious  sulphide. 
Osmium :  as  brownish-black  OsS,  osmic  sulphide 
Rhodium :  as  brown  RhgSg,  rhodic  sulphide. 
Ruthenium :  as  brown  RugSg,  ruthenic  sulphide.      J 
(The  liquid  at  first  becomes  azure-blue  in  color.) 
Gold:  as  black  AugS,  aurous    sulphide,  or  AU2S3, 

auric  sulphide. 
Platinum :  as  brownish-black  PtS2,  platinic  sulphide. 
Iridium :  as  brown  Ir2S3,  iridic  sulphide. 
Molybdenum :  as  brown  M0S3,  molybdic  sulphide. 
(A  small  quantity  of  liydrogcn  sulphide  colors  the 

solution  bhie.) 
Selenium :  as  yellow,  which  on  warming  changes  to 

reddish-yellow  SeS2,  selenic  sulphide. 
Tellnriurn:  as  brown  TeS^,  tolhu'ic  sulphide. 
The  solution  may  become  blue;  in  color  if  compounds  of 

tungsten  or  ranadium  arc  present. 


195 


THIRD  CROUP. 


Ammonium    hydroxide   in   the    presence   of   ammonium 
chloride  precipitates : 

Uranium:   as   yellow   (NH4)2Ur207(?),  ammonium 

uranate. 
Indium :  as  white  In(OH)3,  indie  hydroxide,  soluble 

in  NaOH. 
Beryllium:  as  white  Be(OH)2,  beryllic  hydroxide, 

soluble  in  NaOH. 
Zirconium:  as  white  Zr(OH)4,  zirconic  hydroxide, 

insoluble  in  NaOH. 
Thorium :  as  white  Th(OH)4,  thoric  hydroxide,  in- 
soluble in  NaOH. 
Yttrium:   as  white  Y(OH)2,  yttric  hydroxide,  in- 
soluble in  NaOH. 
Cerium :  ^ 

Lanthanum :  >  as  basic  salts. 
Didymium :    J 

Titanium :  as  white  Ti(OH)4,  titanic  hydroxide. 
Tantalum :  as  white  Ta02(0H),  acid  tantalic  hydroxide, 

or  as  an  acid  ammonium  salt. 
Niobium :  as  white  Nb02(0H),  acid  niobic  hydroxide,  or 
as  an  acid  ammonium  salt. 


FOURTH   GROUP. 


Ammonium  sulphide  precipitates : 

Thallium :  as  black  TI2S,  thallous  sulphide. 

If  the  filtrate  from  the  Fourth  Group  precipitate  is  treated 
with  hydrochloric  acid,  there  will  bo  precipitated : 
Tungsten :  as  brown  W83,  tungstic  sulphide. 


196 

Vanadium:    as    brown    vanadiiuu    sulphide,    containing 

oxygen  and  varying  in  composition. 
Molybdenum:  as  brown  M0S3,  molybdic  sulphide. 

SIXTH    GROUP. 

In  this  group  may  be  found ; 

Lithium. 

Ccesium. 

Rubidium, 
(To  be  detected  by  means  of  the  spectroscope.) 


III.  EXAMPLES  FOR   PRACTICE, 

WOLFRAMITE. 

Wolfmmite  may  be  recognized  by  the  blue  color  it  imparts 
to  the  bead  of  microcosmic  salt  in  the  reducing  flame,  and  by 
the  yellow  residue  of  tungstic  acid  remaining  when  the  finely- 
pulverized  mineral  is  boiled  with  hydrochloric  acid. 

The  finely-pulverized  wolframite  is  boiled  with  concentrated 
hydrochloric  acid,  and  a  few  drops  of  concentrated  nitric 
acid  are  added  from  time  to  time,  until  the  undissolved  resi- 
due is  pure  yellow  in  color  and  does  not  undergo  further 
change.  Tungstic  acid  remains  undissolved  as  a  yellow 
powder,  w^hile  the  bases  enter  into  solution  as  chlorides.  The 
liquid  containing  the  insoluble  residue  is  evaporated  to  dry- 
ness on  a  water-bath,  the  residue  extracted  with  water  con- 
taining a  small  quantity  of  hydrochloric  acid,  filtered,  and 
the  filtrate  tested  for  bases. 

The  insoluble  residue  contains  tungstic  acid,  and  frequently 
silicic  acid  and  niobic  acid.  The  residue  is  treated  with  am- 
monium hydroxide,  which  dissolves  the  tungstic  acid  as  an 


197 

ammonium  salt,  leaving  an  undissolved  residue  consisting  of 
silicic  acid  and  possibly  niobic  acid.  This  residue  is  thor- 
oughly washed  with  ammonium  hydroxide,  to  render  it  free 
from  tungstic  acid,  and  then  tested  in  a  bead  of  microcosmic 
salt  for  niobic  acid. 

The  ammoniacal  solution  containing  ammonium  tungstate 
should  give  the  following  reactions  : 

Hydrochloric  acid  precipitates  white  H2WO4,  tungstic  acid, 
which,  on  boiling,  becomes  yellow. 

Metallic  zinc  and  an  excess  of  hydrochloric  acid  impart 
to  the  precipitate  of  tungstic  acid  a  blue  color  changing  to 
brown  (due  to  the  formation  of  lower  oxides  of  tungsten). 

Stannous  chloride  produces  a  yellow  precipitate ;  on  adding 
hydrochloric  acid  and  warming,  the  yellow  color  changes  to 
blue. 

Ammonium  sulphide  added  to  the  solution  of  ammonium 
tungstate  produces  no  precipitate,  but  forms  the  soluble 
sulpho-salt  (NH4)2WS4.  On  adding  hydrochloric  acid  to  this 
solution,  brown  WSg,  tungstic  sulphide,  is  precipitated.  The 
supernatant  liquid  is  generally  blue  in  color. 


MOLYBDENITE. 

Molybdenite,  when  fused  in  a  bead  of  microcosmic  salt, 
yields  a  colorless  bead  in  the  oxidizing  flame  and  a  black 
bead  in  the  reducing  flame.  It  imparts  a  yellowish-green 
color  to  the  non-luminous  flame.  When  heated  on  cliarcoal, 
it  yields  a  reddish-brown  mass.  It  is  soluble  in  nitro-hydro- 
chloric  acid,  imparting  a  green  color  to  the  liquid.  On 
evaporating  the  excess  of  acid,  diluting  with  water,  and  con- 
ducting hydrogen  sulphide  into  the  solution,  a  blue  coloration 
is  produced,  and  gradually  brownish-black  M0S3,  molybdic 
sulphide,  is   precipitated.     Molybdic  sulphide  is  soluble  in 

17* 


108 

ammonium  sulphide,  which  dissolves  it  as  a  sulpho-salt, 
(NH4)2MoSi,  from  which  solution  it  is  reprecipitated  by 
hydrochloric  acid  as  M0S3,  molybdic  sulphide. 

The  filtrate  from  the  precipitate  produced  by  the  intro- 
duction of  hydrogen  sulphide  may  still  contain  molybdenum 
in  solution ;  therefore,  before  testing  for  the  metals  of  the 
Fifth  Group,  ammonium  hydroxide  is  added  to  the  solution, 
which  is  gently  warmed,  filtered  if  a  precipitate  be  formed, 
and  the  solution,  which  now  contains  (NH4)2MoS4,  is  treated 
with  hydrochloric  acid,  which  precipitates  the  remaining 
molybdenum  as  molybdic  sulphide. 

The  molybdic  sulphide  reprecipitated  in  the  Second  Group 
from  the  ammonium  sulphide  solution  by  hydrochloric  acid 
is  collected  on  a  filter,  dried,  and  placed  in  an  uncovered 
crucible,  which  is  placed  obliquely  over  the  flame  and  gently 
heated,  whereby  the  molybdic  sulphide  is  oxidized  and  con- 
verted into  molybdic  acid,  with  the  evolution  of  sulphurous 
anhydride.  When  the  sulphurous  anhydride  ceases  to  be 
evolved,  the  yellow  residue  is  dissolved  in  ammonium  hy- 
droxide and  the  resulting  solution  of  ammonium  molybdate 
tested  as  follows :  a  small  portion  of  the  solution  is  tested 
for  copper  with  a  few  drops  of  ammonium  sulphide,  and  the 
remainder  of  the  solution  is  used  in  making  the  tests  for 
molybdenum.  (The  precipitated  molybdic  sulphide  obtained 
from  the  Fourth  Group  is  heated  in  an  uncovered  crucible 
and  treated  in  the  same  manner.) 

Hydrochloric  acid  causes  the  precipitation  of  white  H2M0O4, 
molybdic  acid,  soluble  in  an  excess  of  hydrochloric  acid. 
Stannous  chloride  produces  in  the  hydrochloric  acid  solution 
of  molybdic  acid  a  blue  coloration,  changing  to  green  and 
finally  to  brown ;  metallic  zinc  produces  a  similar  coloration, 
but  not  so  promptly.  The  cliange  in  color  in  the  two  pre- 
ceding reactions  is  due  to  the  reduction  of  molybdic  acid. 


199 

Ammonium  sulphocyanide  added  to  the  ammoniacal  solu- 
tion, followed  by  the  addition  of  hydrochloric  acid  and  zinc, 
produces  a  carmine-red  coloration  (in  consequence  of  reduction 
with  the  formation  of  sulphocyanides  of  the  oxides). 

Concentrated  nitric  acid  and  sodium  hydrogen  phosphate 
added  to  the  ammoniacal  solution  precipitate  yellow  am- 
monium phosphomolybdate. 

WULFENITE. 

Wiilfenite,  when  heated  in  the  blowpipe  flame  on  charcoal, 
yields  a  globule  of  metallic  lead ;  when  fused  in  a  bead  of 
microcosmic  salt,  it  yields  a  colorless  bead  in  the  oxidizing 
flauie  and  a  black  bead  in  the  reducing  flame. 

Wulfenite  is  soluble  in  hydrochloric  acid  with  the  sepam- 
tion,  upon  cooling,  of  crystalline  plumbic  chloride.  The 
hydrochloric  acid  solution  yields  with  hydrogen  sulphide  in 
the  Second  Group  a  precipitate  of  molybdic  sulphide,  soluble 
in  ammonium  sulphide,  thus  furnishing  a  means  of  separating 
it  from  plumbic  sulphide,  which  is  insoluble  in  ammonium 
sulphide.  After  precipitating  the  Fourth  Group,  the  reddish- 
brown  filtrate  is  treated  with  hydrochloric  acid  to  precipitate 
the  remainder  of  molybdic  sulphide. 

The  molybdic  sulphide  is  further  examined  as  given  under 
Molybdenite,  page  197. 

URANINITE  (PITCHBLENDE). 

Uraninite,  when  fused  in  the  bead  of  microcosmic  salt, 
yields  a  yellow  bead  in  the  oxidizing  flame  and  a  green  bead 
in  the  reducing  flame ;  treated  Avith  nitric  acid  it  dissolves, 
leaving  a  residue  of  silicic  acid  and  insoluble  oxides  (see  page 
116).  The  nitric  acid  solution  yields  in  the  Third  Group  a 
precipitate  containing  uranium,  the  uranium  being  precipi- 
tated as  vellow  ammonium  uranate.     In  order  to  separate 


200 

uranium  the  precipitate  of  the  Third  Group  is  digested  at  a 
moderate  heat  with  a  concentrated  sohition  of  ammonium 
carbonate ;  uranium  enters  into  solution  as  uranyl  ammonium 
carbonate,  Ur02C03  ((NH4)2C03)2,  imparting  a  yellow  color 
to  the  solution. 

The  oxides  of  the  other  metals  remain  undissolved,  and 
after  being  collected  on  a  filter  may  be  examined  according 
to  the  usual  scheme  of  analysis. 

To  detect  uranium  a  portion  of  the  yellow  filtrate  contain- 
ing uranyl  ammonium  carbonate  is  acidulated  with  acetic 
acid  and  treated  with  potassium  ferrocyanide :  a  reddish- 
brown  precipitate  of  (Ur02)2  Fe(CN)g,  uranyl  ferrocyanide, 
indicates  the  presence  of  uranium.  The  remainder  of  the 
solution  of  uranyl  ammonium  carbonate  is  carefully  concen- 
trated on  a  water-bath,  and  on  cooling  glistening  yellow 
crystals  of  uranyl  ammonium  carbonate  separate,  which  when 
strongly  ignited  leave  a  residue  of  dark-green  uranous-uranic 
oxide,  UrgOg. 

On  treating  the  filtrate  containing  ammonium  sulphide 
from  the  precipitate  of  the  Fourth  Group  with  hydrochloric 
acid,  nickelous  sulphide  together  with  vanadic  sulphide  may 
be  precipitated.  If  a  precipitate  is  obtained  by  treatment  with 
hydrochloric  acid,  it  is  collected  on  a  filter,  washed,  dried, 
mixed  with  potassium  nitrate,  fused,  and  the  resulting  fused 
mass  extracted  with  water,  whereby  vanadium  as  an  acid 
vanadium  salt  enters  into  solution.  On  filtering,  neutralizing 
the  filtrate  with  nitric  acid,  and  adding  a  concentrated  solution 
of  ammonium  chloride,  vanadic  acid  in  combination  with 
ammonium  is  gradually  precipitated  as  a  white  ammonium 
salt.  On  collecting  the  precipitate  on  a  filter,  dissolving  in 
water,  and  adding  a  small  quantity  of  hydrochloric  acid,^^^ 


*  The  solution  becomes  yellow  <»r  r*'d  in  color. 


201 

followed  by  the  addition  of  metallic  zinc,  the  solution  becomes 
blue  in  color. 

RUTILE  (TITANIFEROUS  IRON). 

Rutile,  when  fused  in  a  bead  of  microcosmic  salt  in  the 
reducing  flame,  yields  a  violet-  to  blood-red-colored  bead. 
Fused  in  the  oxidizing  flame  (when  a  sufficient  quantity 
of  the  mineral  is  employed)  it  yields  microscopic  tabular 
crystals  of  anatase  (TiOg). 

The  mineral  is  best  decomposed  by  being  fused  with  acid 
potassium  sulphate  at  not  too  high  a  temperature.  The  fused 
mass  after  cooling  is  pulverized  and  dissolved  in  cold  water : 
the  titanium  enters  into  solution  as  sulphate.  The  liquid  is 
filtered  and  a  portion  of  the  filtrate  tested  with  metallic  zinc 
or  tin  for  titanic  acid :  in  the  presence  of  titanic  acid  a 
pale  violet  or  a  blue  coloration  is  imparted  to  the  solution 
and  afterwards  a  blue  precipitate  separates  which  gradually 
changes  to  white. 

On  boiling  the  remainder  of  the  precipitate  for  some  time, 
me ta- titanic  acid  separates  as  a  white  powder.  The  meta- 
titanic  acid  is  filtered  oif  and  the  filtrate  diluted  with  water 
and  again  boiled  and  filtered.  The  filtrate  is  then  tested  for 
the  remaining  bases  in  the  usual  manner. 

BERYL. 

Beryl,  when  fused  in  a  bead  of  microcosmic  salt,  slowly 
dissolves  without  the  formation  of  a  skeleton  of  silica.  The 
fragment  of  beryl  remains  in  the  bead  of  microcosmic  salt 
and  gradually  diminishes  in  size,  forming,  on  cooling,  an 
opalescent  bead.  Varieties  of  beryl  containing  chromium 
(for  example,  emeralds)  impart  a  green  color  to  the  bead. 

As  beryl  is  insoluble  in  acids,  it  must  be  decomposed  by 
fusing  with  sodium  potassium  carbonate.     The  fused  mass  is 


202 

treated  with  hydrochlorie  acid  and  evaporated  to  dryness  on 
a  water-bath,  in  order  to  separate  silicic  acid.  The  residne 
is  extmcted  with  water  containing  a  small  quantity  of  hydro- 
chloric acid  and  filtered  ;  the  filtrate  contains  BeClg,  beryllium 
chloride.  On  the  addition  of  ammonium  hydroxide  to  the 
filtrate,  Be(OH)2,  beryllium  hydroxide,  separates  as  a  white 
precipitate,  and  is  collected  on  a  filter  and  dissolved  in  an 
excess  of  sodium  hydroxide.  The  sodium  hydroxide  solution 
contains  sodium  aluminate  and  sodium  beryllate,  and  may 
also  contain  sodium  chromite,  in  which  case  the  solution 
would  be  green  in  color. 

If  chromium  is  not  present,  the  solution  is  treated  with  a 
considerable  quantity  of  ammonium  chloride,  which  precipi- 
tates aluminium  hydroxide  and  beryllium  hydroxide.  On 
boiling  the  liquid  for  some  time,  beryllium  hydroxide  enters 
into  solution  as  beryllium  chloride,  with  the  evolution  of 
ammoniacal  gas,  while  aluminium  hydroxide  remains  un- 
dissolved, is  collected  on  a  filter,  and,  when  lieated  with 
cobaltous  nitrate  on  charcoal,  yields  a  blue  mass.  The  fil- 
trate, which  contains  beryllium  chloride,  is  treated  with 
ammonium  hydroxide  to  precipitate  beryllium  hydroxide. 
Beryllium  hydroxide  is  soluble  in  an  excess  of  ammonium 
carbonate,  and  from  this  solution  it  separates  on  boiling  as  a 
basic  bervllium  carbonate.  The  bervllium  hydroxide,  when 
heated  with  cobaltous  nitrate  in  the  oxidizing  flame  on  char- 
coal, yields  a  gray  mass. 

If  chromium  is  present,  the  solution  is  diluted  with  water 
and  boiled  for  some  time :  aluminium  hydroxide  remains  in 
solution,  while  beryllium  hydroxide  and  chromium  hydroxide 
are  precipitated.  The  precij)itate  is  collected  on  a  filter, 
dried,  and  the  beryllium  hydroxide  separated  from  the  chro- 
mium hydroxide  by  fusing  with  a  mixture  of  sodium  carbon- 
ate and  potassiiuii  nitrate.     On  extracting  the  yellow  fused 


203 

mass  with  water,  beryllium  oxide  remains  undissolved,  while 
chromium  enters  into  solution  as  a  chromate  of  the  alkali. 

CERITE. 

Cerite,  heated  in  the  blowpipe  flame  on  charcoal,  is  infusi- 
ble, but  becomes  dirty  yellow  in  color.  Fused  in  a  bead  of 
microcosmic  salt,  it  yields  in  the  oxidizing  flame  a  reddish- 
yellow  bead,  and  in  the  reducing  flame  a  colorless  l^ead, 
together  with  a  skeleton  of  silica.  On  heating  a  portion  of 
the  finely-pulverized  mineral  with  hydrochloric  acid,  diluting 
with  water,  filtering,  and  adding  oxalic  acid  to  the  filtrate,  a 
white  precipitate  is  produced. 

On  heating  the  mineral  with  concentrated  hydrochloric 
acid,  evaporating  to  dryness  on  a  water-bath,  and  extracting 
the  residue  with  Avater  and  a  few  drops  of  hydrochloric  acid, 
the  bases  enter  into  solution  while  silicic  acid  remains  undis- 
solved. 

In  the  Second  Group,  in  addition  to  other  metals,  molyb- 
denum may  be  precipitated  as  molybdic  sulphide.  (See 
Molybdenite,  page  197.) 

Cerium,  lanthanum,  and  didymium  are  precipitated  by 
ammonium  hydroxide  in  the  Third  Group  as  hydroxides : 
Ce(OH)2,  La(OH)2,  and  Di(OH)2.  Cerium  hydroxide  and 
lanthanum  hydroxide  are  white.  The  former  when  exposed 
to  the  air  oxidizes  and  becomes  yellow  ;  didymium  hydroxide 
is  pink  in  color.  On  collecting  the  precipitate  of  the  Third 
Group  on  a  filter,  dissolving  in  hydrochloric  acid,  and  add- 
ing oxalic  acid,  cerium,  lanthanum,  and  didymium  are  pre- 
cipitated as  white  oxalates  insoluble  in  dilute  acids ;  the 
filtrate  from  the  precipitate  of  oxalates  may  be  examined  for 
the  remaining  bases  of  the  Third  Group. 

The  oxalates  of  cerium,  lanthanum,  and  didymium  when 
ignited  yield   a    brown   residue   consisting  of  a   mixture  of 


204 

oxides  (Cefi^,  LaO,  and  DiO).  On  heating  a  portion  of 
this  mixture  of  oxides  with  concentrated  sulphuric  acid,  sul- 
phates are  formed  which  are  soluble  in  water  and  impart  a 
yellow  color  to  the  liquid.  In  this  solution  concentrated 
potassium  sulphate  produces  a  lemon-yellow  precipitate  con- 
sisting of  a  mixture  of  double  salts. 

The  remainder  of  the  mixture  of  oxides  is  treated  with 
hydrochloric  acid  and  alcohol  and  then  heated :  the  oxides 
are  dissolved  thereby,  with  the  formation  of  chlorides  (CeCl2, 
LaCl2,  DICI2).  If  didymium  is  present,  on  passing  a  ray  of 
light  through  the  solution,  the  spectrum  shows  dark  absorp- 
tion bands  (four  between  Frauenhofer's  lines  D  and  F  and 
two  between  F  and  G). 

On  adding  sodium  acetate  and  passing  chlorine  through 
the  solution,  or  on  the  addition  of  sodium  hypochlorite,  light- 
yellow  CcgOyllg,  cerium  hydroxide,  is  precipitated,  Avhich  is 
soluble  when  warmed  with  hydrochloric  acid,  forming  CeClg, 
with  the  evolution  of  chlorine.  (For  the  separation  of 
cerium,  lanthanum,  and  didymium  the  reader  is  referred  to 
more  extensive  works  on  qualitative  analysis.)  '     ' 

ZIRCON   (HYACINTH). 

Zircon,  heated  in  the  blowpipe  flame  on  charcoal,  is  infusi- 
ble, but  becomes  lighter  in  color.  It  is  not  dissolved  in  the 
bead  of  microcosm ic  salt. 

It  is  decomposed  by  being  fused  for  some  time  with  sodium 
potassium  carbonate.  The  fused  mass  is  treated  with  hydro- 
chloric acid,  evaporated  to  dryness  on  a  water-bath  (to  render 
the  silica  insoluble),  the  residue  extracted  with  water  and 
hydrochloric  acid  and  filtered.  The  filtrate  contains  zirco- 
nium as  zirconium  chloride.  From  this  solution  the  zirco- 
nium is  precipitated  by  ammonium  hydroxide  in  the  Third 
Group   as    Zr(OH)4,  zirconium   hydroxide.     Zirconium   hy- 


205 

droxide  is  insoluble  in  sodium  hydroxide,  but  soluble  in 
ammonium  carbonate.  From  the  solution  in  ammonium 
carbonate  it  is  reprecipitated  by  boiling. 

On  dissolving  a  portion  of  this  precipitate  in  sulphuric 
acid  and  adding  a  concentrated  solution  of  potassium  sulphate, 
a  wliite  double  salt  of  zirconium  is  precipitated. 

The  hydrochloric  acid  solution  is  not  precipitated  by  oxalic 
acid,  but  the  neutral  solution  is  precipitated  by  ammonium 
oxalate  ;  the  precipitate  redissolves  in  an  excess  of  ammonium 
oxalate.  Turmeric  paper,  moistened  with  the  hydrochloric 
acid  solution,  becomes  reddish  brown  in  color  when  drv. 

LEPIDOLITE. 

Lepidolite  when  fused  in  a  bead  of  microcosmic  salt  yields 
a  skeleton  of  silica.  When  placed  on  a  platinum  wire  and 
held  in  the  non-luminous  flame  it  imparts  a  carmine-red  color 
to  the  flame,  especially  after  moistening  the  lepidolite  with  a 
few  drops  of  hydrochloric  acid.  Treated  with  concentrated 
sulphuric  acid  it  responds  to  the  fluorine  reactions  (see  4,  page 
82). 

A  portion  of  the  mineral  is  heated  in  a  platinum  crucible 
(without  the  addition  of  carbonates  of  the  alkalies  as  a  flux) 
until  melted.  The  fused  mass  is  pulverized  and  then  decom- 
posed by  being  boiled  with  concentrated  hydrochloric  acid. 
The  solution  is  evaporated  to  dryness  on  a  water-bath  to 
render  the  silica  insoluble ;  the  residue  is  extracted  with 
water  and  a  few  drops  of  hydrochloric  acid,  the  insoluble 
silica  filtered  ofl^,  and  the  filtrate  examined  for  bases. 

Lithium  belongs  to  the  Sixth  Group.  The  hydrochloric 
acid  filtrate,  obtained  as  described  above,  is  treated  with  am- 
monium carbonate  to  precipitate  tlic  metals  of  the  Fifth 
Group,  and  with  sodium  hydrogen  phosphate  to  precipitate 
magnesium,  filtered,  the  filtrate  treated  with  barium  chloride, 

18 


206 

and  the  liquid  again  filtered.  The  filtrate  now  contains,  in 
addition  to  the  excess  of  barium  chloride,  the  alkaline  metals 
as  chlorides.  The  liquid  is  evaporated  to  dryness,  the  residue 
gently  heated  over  a  free  flame  to  expel  ammonium  chloride, 
and  then  placed  in  a  small  flask  and  extracted  with  a  mixture 
of  alcohol  and  ether.  Lithium  chloride  enters  into  solution, 
while  the  chlorides  of  the  other  metals  remain  undissolved. 

The  alcoholic  solution  is  filtered  and  the  filtrate  evaporated 
to  dryness  on  a  water-bath ;  the  residue  remaining  consists 
of  lithium  chloride,  which  is  recognized  by  its  imparting  a 
carmine-red  color  to  the  non-luminous  flame  and  by  the 
examination  with  the  spectroscope.  The  residue,  insoluble 
in  the  mixture  of  alcohol  and  ether,  is  dissolved  in  water, 
and  sulphuric  acid  added  to  the  solution  to  precipitate  barium 
as  barium  sulphate,  which  is  filtered  off  and  the  filtrate  ex- 
amined for  potassium  and  sodium. 

THORITE. 

Thorite  when  fused  in  a  bead  of  microcosmic  salt  is  dis- 
solved with  the  production  of  a  skeleton  of  silica ;  the  bead 
is  colored  yellow,  due  to  ferric  oxide  (and  uranium  oxide), 
and  is  opalescent  while  cooling. 

The  finely  pulverized  mineral  is  heated  with  hydrochloric 
acid,  evaporated  to  dryness,  the  dry  residue  moistened  with 
hydrochloric  acid  and  extracted  with  hot  water  and  the  liquid 
filtered.  The  filtrate  is  treated  with  hydrogen  sulphide  and 
the  precipitated  sulphides  removed  by  filtration.  The  filtrate 
is  treated  with  ammonium  hydroxide,  the  precipitate  which 
is  produced  is  washed,  by  decantation,  with  water  (test  the 
filtrate),  and  then  the  precipitate  is  dissolved  in  hydrochloric 
acid  and  the  solution  treated  with  oxalic  acid.  The  precipi- 
tate produced  is  washed,  by  decantation,  witli  hot  water  (test 
the  filtrate),  and  finally,  after  having  been  boiled  with  water, 


207 

is  collected  on  a  filter,  dried,  and  decomposed  by  incinera- 
tion. 

The  thorium  oxide  thus  obtained  still  contains  oxides  of 
cerium  and  ytterbium  (and  some  manganese).  It  is  now 
treated  with  sulphuric  acid,  and  the  mixture  heated  to  expel 
the  excess  of  sulphuric  acid,  and  the  residue,  consisting 
of  sulphates,  is  dried.  The  residue  is  then  dissolved  in 
ice-cold  water,  and  the  solution  allowed  to  become  of  the 
temperature  of  the  room,  whereby  thorium  sulphate,  contain- 
ing water,  separates  while  the  sulphates  of  cerium  and  ytter- 
bium remain  in  solution.  The  supernatant  liquid  is  removed 
by  decantation,  the  thorium  sulphate  is  collected  on  a  filter, 
washed  with  water,  removed  from  the  filter,  and  by  careful 
heating  rendered  free  from  the  water  it  contained.  The 
thorium  sulphate  is  now  dissolved  in  ice-cold  water,  and 
from  this  solution  the  thorium  is  precipitated  as  Th(OH)^ 
thorium  hydroxide,  by  the  addition  of  ammonium  hydroxide. 

LEAD    SELENIDE. 

Lead  selenide  occasionally  decrepitates  when  heated  in  a 
reduction  tube,  but  undergoes  no  further  change.  When 
heated  in  a  glass  tube  open  at  both  ends  selenium  is  given 
oif,  which  collects  as  a  gray  sublimate  near  the  heated  part 
of  the  tube,  and  as  a  red  sublimate  in  the  part  of  the  tube 
beyond  the  gray  sublimate ;  at  the  same  time  an  odor  resem- 
bling that  of  decayed  radishes  is  produced.  When  heated 
on  charcoal  it  produces  fumes  having  an  odor  similar  to  that 
of  decayed  radishes,  fuses  only  imperfectly,  and  covers  part 
of  the  charcoal  with,  primarily,  an  incrustation  of  selenium 
which,  near  the  point  where  the  heat  was  applied,  is  black, 
and  at  the  outer  edges  red  ;  eventually,  on  continuing  the 
heat,  an  incrustation  of  lead  oxide  is  formed.  On  prolonged 
used  of  the  blowpipe  flame  considerable  volatilization  occurs. 


208 

until  finally  a  very  small  fused  mass  remains  which,  when 
portions  are  tested  in  the  bead  of  microcosmic  salt,  occasion- 
ally furnishes  evidence  of  the  presence  of  iron,  cobalt,  or 
copper.  Fused  with  sodium  carbonate  or  charcoal,  lead  sel- 
enide  produces  a  brownish-red  mass,  which  on  further  fusion 
yields  metallic  lead,  which  occasionally  contains  silver.  (On 
heating  the  globule  of  lead  on  a  cupel  of  bone  ash  to  remove 
the  lead  by  absorption,  a  small  globule  of  silver  will  remain, 
provided  it  was  present  in  the  lead  selenide  employed.) 

The  very  finely  pulverized  mineral  is  treated  with  dilute 
hydrochloric  acid  to  remove  calcite  and  siderite.  The  resi- 
due is  collected  on  a  filter  and  washed  with  water,  and  then 
it  is  digested  with  nitric  acid,  whereby  PbSeOg,  plumbic  sel- 
enate,  is  produced.  The  solution  thus  obtained  is  evaporated 
to  expel  the  nitric  acid,  and  the  residue,  consisting  of  plumbic 
selenate,  is  treated  with  dilute  sulphuric  acid,  whereby  insol- 
uble plumbic  sulphate  is  produced,  and  soluble  H2Se03, 
selenic  acid,  remains  in  solution.  The  plumbic  sulphate  is 
removed  by  filtration,  and  the  filtrate  is  diluted  with  water 
and  a  current  of  sulphurous  anhydride  is  passed  through, 
whereby  sulphuric  acid  is  produced  and  selenium  separates 
as  a  red  powder : 

PbSe  -f  2HNO3  =  PbSeOa  +  H^O  +  2NO ; 

PbSeOg  +  H2SO4  =  PbSO^  +  H^SeOg ; 

H^SeOg  H-  2SO2  +  H2O  =  2H2SO,  +  Se. 


INDEX. 


PAGE 

Acetates 103,  190 

Acetic  acid 103,  190 

Acid,  acetic      103,  190 

arsenic 84 

arsenious 29 

boric 80,  184 

carbonic 83,  184 

chloric 102,  190 

chromic 86,  185 

ferricyanic 96,  187 

ferrocyanic 95,  187 

hydriodic      ...        91,  186 

hydrobromic 90,  186 

hydrochloric 88,  186 

hydrocyanic 93,  186 

hydroferricyanic 96,  187 

hydroferrocyanic 95,  187 

hydrofluoric 81 

hydrofluosilicic 74,  182 

hypochlorous 100,  189 

hyposu^phurous      77,  183 

molybdic 194 

niobic 191 

nitric 101,  189 

nitrous      99,  189 

oxalic 104 

phosphoric 78,  185 

silicic 84,  184 

sulphocyanic 97,  188 

sulphuric      73,  182 

sulphurous 75,  182 

sulphydric 98,  188 

tantalic l-*4 

0  18*     •  20<» 


210 

PAGE 

Acid,  tartaric 105,  18") 

thiosulphuric 77 

titanic 191 

Acid  sulphides,  separation  of 152 

Acids,  behavior  with  group  reagents .  178 

examination  for 174 

preliminary  tests  for 116 

Aluminium 5q 

Ammonium 72 

carbonate 62 

Antimony 36 

Marsh's  test  for 3j^ 

Keinsch's  test  for 39 

in  antimonic  condition      40 

in  antimonious  condition 37 

Arsenic 28 

Marsh's  test  for 30 

Keinsch's  test  for 33 

in  arsenic  condition 34 

in  arsenious  condition 29 

Arsenic  acid 34 

Arsenious  acid 29 

Barium 64 

Bases,  detection  of,  in  the  Wet  Way 133 

precipitation  of  groups 133 

properties  of 15 

separation  of  First  Group 146 

Second  Group 148 

Third  Group 159 

Fourth  Group 164 

Fifth  Group 165 

Sixth  Group 168 

Basic  sulphides,  separation  ol 150 

Beryl 201 

Beryllium 195 

Bismuth 27 

Borates 80,  184 

Boric  acid 80,  184 

Bromides      90,  188 


211 

PAGE 

Cadmium 43 

Caesium 196 

Calcium 65 

Carbonates 83,  184 

Carbonic  acid 83,  184 

Cerite 203 

Cerium ]95 

Charcoal,  examination  on HO 

Chlorates 102,  190 

Chloric  acid 102   190 

Chlorides 88,  186 

Chromates 86,  185 

Chromium 52 

Cobalt 58 

Copper     24 

Cyanides 93^  128,  186 

Detection  of  bases  in  the  Wet  Way 133 

Didymium I95 

Dissolving  metals  and  alloys 127 

oxides  and  salts 121 

Everett's  salt 48,  95 

Examination  by  microcosmic  salt 114 

for  acids 174 

in  the  flame 114 

in  the  reduction-tube 107 

on  charcoal 110 

Ferricyanides 96,  187 

Ferrocyanides      95,  187 

Flame,  examination  in 114 

Fluorides 81 

Gold      ^ 

Group  (acids) : 

First 73 

Second 75 

Tnird ^8 

Fourth      101 


212 

Group  (bases) :  page 

First     15 

Second      22 

Third 46 

'     Fourth 54 

Fifth 62 

Sixth 66 

Group  precipitations,  table  of 134 

Beavy  metals,  sulphides  of 128 

Hyacinth     204 

Hydriodic  acid 91,  186 

Hydrobromic  acid 90,  186 

Hydrochloric  acid 88,  186 

Hydrocyanic  acid 93,  186 

Hydroferricyanic  acid 96,  187 

Hydroferrocyanic  acid 95,  187 

Hydrofluoric  acid 81 

Hydrofluosilicic  acid      74,  182 

Hydrogen  sulphide 98,  188 

Hypochlorites      100,  189 

Hypochlorous  acid 100,  189 

Hyposulphites 77,  183 

Hyposulphurous  acid 77,  183 

Indium 195 

Iodides 91,  186 

Iridium 194 

Iron 47 

in  ferric  condition 49 

in  ferrous  condition 47 

Lanthanum 195 

Lead 19 

Lead  selenide 207 

Lepidohte 205 

Lithium 72 

Magnesia  mixture 78 

Magnesium      ...        •    ■      66 

Manganese 55 


213 

PAGE 

Marsh's  test , 30 

Mercury 17 

in  mercuric  condition 22 

in  mercurous  condition 17 

Metals  and  alloys,  dissolving  of 127 

Microcosmic  salt,  examination  by      114 

Molybdenite 197 

Molybdenum 194 

Nickel 61 

Niobium 195 

Nitrates 101,  189 

Nitric  acid 101,  189 

Nitrites 99,  189 

Nitrous  acid 99,  189 

Organic  acids .  103 

Osmium 194 

Oxalates 104 

Oxalic  acid 104 

Oxides  and  salts,  dissolving  of 121 

Palladium .  194 

Phosphates 78,  183 

Pitchblende 199 

Platinum 46 

Potassium »    .   •    .  69 

Precipitation  of  the  bases : 

First  Group 136 

Second  Group     .    , 139^ 

Third  Group ••    •  141 

Fourth  Group     .    „ 143 

Fifth  Group 144 

Sixth  Group 145 

Preliminary  examination •    •  107 

tests  for  acids 116 

tests  in  the  Dry  Way •    •  1^7 

Properties  of  the  acids •    •  73 

of  the  bases •    •  1^ 

Prussian  blue 49,  9b 


214 

PAGE 

Rare  elements,  behavior  of 191 

preliminary  teste  for 191 

Reinsch's  test 33 

Rhodium 194 

Rubidium 196 

Ruthenium 194 

Rutile 201 

Selenides 191 

Selenium 194 

Separation  of  acid  sulphides 152 

of  bases :  First  Group 146 

Second  Group 148 

Third  Group .    159 

Fourth  Group 164 

Fifth  Group 165 

Sixth  Group .    168 

of  basic  sulphides 150 

Silicates 84,  130,  184 

Silicic  acid 84,  184 

Silicofluorides 74,  182 

Silver 15 

Sodium 70 

Solubilities,  table  of 180 

Strontium 64 

Sulphates 73,  182 

Sulphides 98,  188 

of  heavy  metals 128 

Sulphites 75,  182 

Sulphocyanates 97,  188 

Sulphocyanic  acid 97,  188 

Sulphocyanides 97,  188 

Sulphuric  acid 73,  182 

Sulphurous  acid 75,  182 

Sulphydric  acid 98,  188 

Table  of  group  precipitations 135 

Table  of  solubilities 180 

Tantalic  acid 194 

Tantalum 195 


215 

PACK 

Tartaric  acid 105 

Tartrates lOo 

Tellurium 194 

Tests,  preliminary,  in  Dry  Way 107 

Thallium 194 

Thenard's  blue 52 

Thiosulphates     77 

Thiosulphuric  acid 77 

Thorium 195 

Thorite 206 

Tin 41 

in  stannic  condition 42 

in  stannous  condition 41 

Titanic  acid 191 

Titaniferous  iron 201 

Titanium 195 

TurnbuU's  blue 48,  96 

Uraninite 199 

Uranium      195 

Vanadium 196 

Wolframite     196 

Wulfenite 199 

Yttrium 195 

Zinc 57 

Zircon 204 


